Here Are the Most Common Heating Issues that Happen During the Winter

Williams Comfort Air - Tech working on HVAC unit

Cincinnati, Ohio area homeowners expect cold temperatures and plenty of snow during winter. To make your home comfortable and safe, you rely on your furnace around the clock. While having a functional heat pump, gas furnace, or boiler is essential, you can’t always predict when that essential appliance will act up.

While some heating problems are incredibly common and easy to troubleshoot on your own, others need to be professionally addressed immediately to prevent heating outages on frigid days. Being able to quickly and efficiently identify and resolve heating concerns is essential, especially when you have a family that relies on you to create a safe environment.

At Thomas & Galbraith Heating, Cooling & Plumbing, we are committed to keeping our neighbors throughout the greater Cincinnati Metro area as warm and cozy as possible through fast, efficient, and reliable service. With a team of NATE-certified technicians who are committed to empowering our clients with valuable information, we help you avoid issues with your furnace or heating system so you are able to enjoy the important things that come with the winter season.

One element that sets our team apart is our innate understanding of the heating issues that tend to impact clients throughout Cincinnati and the surrounding communities. This complimentary, comprehensive guide is designed to help homeowners understand and resolve heating problems, making your day a little easier. Whether you need to do a few things on your own or reach out to a professional for furnace troubleshooting, use this guide to learn exactly what that issue may mean and how to fix it. When you’re able to take control of the situation, you stress less, enjoy a more comfortable environment, and stay safer this winter.

How to Use this Guide

This heating guide outlines issues you may experience with your furnace or heat pump over the course of heating season. Below, find common symptoms of heating troubles, explanations of what could be causing those issues inside your heat pump, or furnace, and what you should do to fix the problem. Learn simple troubleshooting techniques for harmless symptoms and find out when professional service is required. If DIY repair isn’t an option for a particular repair, find out how technicians may approach an issue to solve it now and prevent ongoing problems.

20 Common Winter Heating System Issues

The next time you experience heating issues at home, search this list of furnace problems to learn what could cause that symptom. Better yet, familiarize yourself with this list, so you know what to do the next time your furnace or heat pump does something new and unexpected.

1. Heating system won’t switch on

When furnaces don’t turn on immediately after the thermostat is switched to “heat,” it can be nerve-wracking. When facing this common furnace problem, homeowners may fear that their system is failing or has already died. However, this common problem doesn’t necessarily mean that your furnace or heat pump is doomed. Sometimes, minor issues prevent your system from turning on. If your furnace does not switch on at all when it’s time to heat the home, the causes could be:

  • Heating equipment not receiving power. Heating units, even gas furnaces, require electricity to operate the ignition and to regulate the motor. If no power reaches your heating system, your furnace does not activate appropriately. Sometimes, the problem is as simple as a tripped breaker or an exterior power switch on the air handler, furnace, or heat pump is turned off. Check all power sources associated with your furnace or heat pump to make sure they are set properly before you try starting the system again. If there are no power outages in your area but your furnace won’t turn on, place a service call.
  • Ajar access door. As a safety precaution, many furnaces will not operate if the blower compartment door is open. Systems are designed this way to prevent fire hazards and damage to the blower components. If your furnace or air handler won’t switch on, check the panels on the unit’s exterior to ensure they are closed tightly.
  • Thermostat not receiving power. Your thermostat is charged with the task of relaying information from your home to the furnace or heat pump. However, if the thermostat itself doesn’t receive power, it won’t be able to tell the system to start up or shut down. Check the thermostat display to see if it is turned on, operating properly, and displaying any error messages. If the display is blank, check to see if batteries need to be replaced and that the electrical connections are tight so the thermostat is able to relay data. If the thermostat is hardwired, check the breaker that controls the area.
  • Incorrect thermostat settings. Sometimes, furnaces don’t switch on for the simple fact that the thermostat may be set improperly. Ensure that the system is on the HEAT setting and check the programmed temperature settings. Update the date and time on your thermostat to keep your system operating as it should.

2. Furnace does not ignite

When you turn on your furnace, the system should activate as soon as the set temperature on the thermostat is reached. After the thermostat relays the message to the ignition system, the burners start and the heating process begins. However, if there is an issue with the ignition system, your home won’t receive the heat it needs. Here are some reasons your furnace may not ignite properly.

  • Malfunctioning or damaged ignitor. Over time, ignitors can develop damage from wear and tear. When ignitors become damaged, they may malfunction, and fail to turn on the furnace. Testing and replacing an ignitor is not a DIY job and should be left to a professional. HVAC technicians test ignitors for electrical conductivity using a multimeter and replace malfunctioning components.
  • Incorrect ignitor installed. Different makes and models of furnaces require different ignitors. If the incorrect ignitor is installed in your system, the voltage may not be appropriate, which can cause the system to fail. If your furnace does not ignite, check the service logs for your system to see if the igniter has been replaced. If it was replaced recently, check to make sure that the installed igniter matches the recommended unit for the system. If it doesn’t, or you can’t find the information, have an HVAC technician inspect the component.
  • Dirty electronic ignition. Since ignitors generate a flame, carbon builds up on the unit and dirties the surface over time. When this happens, the system may generate a repetitive clicking sound, and fail to ignite. Since ignitors are delicate, don’t attempt to clean the unit yourself. Ask a professional to clean your ignitor and check it for damage.
  • Pilot light is out. While most modern heating systems don’t use a pilot light, furnaces more than ten years old may rely on standing pilot light ignition. These types of units have a continuously burning flame ready to light the controlled, released fuel when the system is turned on. Check the owner’s manual for your furnace to learn how to turn on the pilot light, and exercise extreme caution. If you light the pilot and it continues to extinguish on its own, check the area for drafts. If an open window or door isn’t blowing out the flame, your furnace could have a faulty thermocouple or gas regulator that should be checked or replaced by a pro.
  • Cracked hot surface ignitor element. Since heat causes expansion, it is possible for the hot surface ignitor’s heating element to crack and fail to ignite the furnace. Hot surface ignitor elements have a lifespan of around 3 to 5 years with proper furnace use, or less time if the system hasn’t been maintained or has a tendency to short cycle. If the unit is cracked, you may be able to replace it carefully with instructions from your service manual, or by calling an HVAC technician.
  • Damaged limit switch. Limit switches are designed to shut off the ignitor inside your furnace when the internal temperature becomes too high. However, if the limit switch malfunctions, it can disrupt ignition. Issues with dirty air filters and airflow blockages also cause overheating, which forces the system to shut down prematurely. Try replacing your furnace filter first. If that doesn’t correct the problem, call on an HVAC technician to check the limit switch – if it is damaged, a new component is needed.

3. Low or no airflow from vents

If your system isn’t delivering adequate amounts of heat to the rooms throughout your home, airflow issues could be at fault. Here are a few causes of impeded airflow.

  • Closed vent registers. To make it easier to control the flow of air into a room, some vent covers have adjustable louvers to allow homeowners to open or close vents. Unfortunately, some louvers are easy to close and they may be unintentionally shut or partially closed. If you don’t have enough airflow coming from the vents in your home, check the covers to see if the louvers are on the “open” position. If louvers are broken or stuck closed, try cleaning the cover or consider replacing it. These components are inexpensive and available at most hardware stores.
  • Clogs in ductwork. Duct systems rely on a series of duct runs to deliver heated and cooled air throughout your home. When ducts are obstructed, air volume through vents is dramatically reduced or stopped altogether, and heat will not reach its destination. Air ducts can become obstructed because of damage, disconnections, or heavy amounts of dust and debris clogging the duct. If you have rooms that are not receiving heated air and you are able to easily access the ducts in your home, check the supply lines to see if they are damaged or disjointed. Some poor connections may be repaired with simple aluminum foil tape. If you can’t find a visible problem, consider ordering duct cleaning and have a professional inspect your duct system for damage.
  • Dirty furnace filters. Furnace filters screen fine particulates out of the air as it circulates through your home. When filters become dirty, they limit airflow, which decreases air volume blowing into rooms. Check your furnace filters every month and replace them when they are visibly dirty. Air filters should be replaced at regular intervals, which for many homes is once every three months.
  • Leaks in ductwork. Duct leaks are estimated to account for 20% to 30% of lost heated and cooled air in the average home. When air is lost, it escapes into areas in your home where it won’t be used, such as the inside of your walls, or in the attic or crawlspace. Seal any visible leaks in ducts with aluminum foil tape. If the problem persists, request professional duct sealing to identify and resolve leaks.
  • Blower motor issues. Your heater’s blower motor moves heated air throughout ducts and into your home. If your blower motor develops a buildup of dirt or grime, a broken fan belt, worn motor bearings, a faulty capacitor, a damaged fan belt pulley, or damage to the electrical component, it may not move air properly. While some of these issues can be resolved easily, such as dusting off the blower motor interior, others may need to be addressed professionally. Experts may need to replace individual components or install a new motor.
  • Damper malfunctions. Some HVAC duct systems contain either automatic or manual damper valves to give homeowners more control over airflow regulation. However, when louvers become stuck in a closed or partially closed position, the damper impedes airflow. Check manual dampers to make sure they are in the open position. If you have an automatic system, the thermostat may control the dampers. If this is the case, a professional diagnosis and repair may be necessary, since there could be a connectivity issue between elements of your damper system and your thermostat.
  • Inadequate or blocked air returns. Your entire HVAC system is balanced with air returns to regulate the temperature throughout your home. When air returns become blocked, or when there are not enough air returns, air pressure decreases. Check air return vents in your home and pull furniture or stored items away from the area to improve airflow. If you can’t find very many air returns, have a professional evaluate your system.

4. Adjusting your thermostat doesn’t do anything

When you switch on your thermostat or increase the temperature in your home, your furnace or heat pump should respond appropriately. However, if your thermostat doesn’t trigger your heating system or if the temperature never seems to increase to the targeted setting, these problems may be at fault for this top furnace problem.

  • Heating equipment not powered. Your thermostat relies on power from your home’s electrical system to communicate heating and cooling needs to the HVAC system. If the breaker that controls your furnace or heat pump is tripped or the fuse has blown, your system doesn’t receive power will not turn on – without power, it’s unable to receive relays from your thermostat. Check your breaker to ensure it isn’t tripped and that fuses are in good condition. Make sure ON/OFF switches on indoor furnaces and air handlers as well as outdoor heat pumps are situated in the “ON” position.
  • Improper thermostat location placement. Thermostats should never be placed in an area prone to steep temperature fluctuations or stagnant air. Thermostats should be placed on an internal wall away from drafts, heavy lighting, kitchen equipment, and storage areas. Thermostats should never be placed in closets or pantries, because this placement would interfere with their ability to read the ambient air temperature. Find your thermostat and look up the placement instructions in your user manual to see if it is in an appropriate spot. If the unit needs to be moved, get professional help.
  • Unlevel or improperly installed thermostat. Thermostats need to be seated into their cradle properly to function. If the thermostat is unlevel due to careless placement or damaged mounting, it could prevent a good pin connection between the unit and the backplate, making your thermostat useless. Remove the thermostat from its cradle and place it into the mounting again to ensure a tight fit. If you can tell that the unit isn’t seating, ask a technician to repair the mount.
  • System set to “AUTO”. Many thermostats have an AUTO mode, which allows the thermostat to run according to programmed setpoints – this is different from the AUTO setting for fan control. When AUTO is selected, you may not be able to activate your furnace or change the temperature. Try switching your unit back to HEAT to adjust temperatures.
  • Locked digital thermostat. Digital thermostats sometimes have a lock setting, giving parents and property owners more control over heat settings. Check your thermostat to make sure it isn’t in the locked position and follow the owner’s manual to learn how to disable lock mode.
  • Internal wiring issues. If dirt and grime accumulate on the wiring inside the thermostat, it can inhibit communication from the device. Loose electrical connections or corroded wires can also disable the system. After removing your thermostat, dust it off carefully with canned air. Tighten connections that seem loose. If the system has visibly damaged wiring, consider a replacement or request a professional repair.

5. Cool air blows from vents when furnace operates

When your system is emitting cool air instead of warm air and it seems like the heating system is on, it could be caused by these issues.

  • Shut gas valve. If you have a gas furnace, a closed gas line prevents fuel from moving into the ignition system properly, so it doesn’t receive fuel for combustion. While the blower system may continue to run, the air that comes from your vents will feel cool. Check your gas valve to ensure that it is in the in the appropriate position. Open valves run in line with the pipe, and closed valves are perpendicular to the line. If the valve is stuck in the off position, it may need to be professionally replaced.
  • Incorrect blower fan settings. Your system may also blow cool air if the blower motor is set to the “ON” position instead of the “AUTO” setting. When the blower fan is set to “ON,” the heating system continues to circulate air, but only starts a heating cycle when the thermostat temperature dips to the setpoint. Keep your thermostat setting on “AUTO” to avoid this problem.
  • Malfunctioning ignition. Like your vehicle, your furnace will not start if the ignition isn’t working. Ignition sparks the flame and initiates the heating process, but if your pilot light isn’t working or the inner components of the ignitor are damaged, your furnace won’t be able to generate heat. For more information about furnace ignition, refer to section 2 of this guide. If the ignition system fails to initiate, no flame is produced in the burners to combust heating fuel. If the ignition is at fault, how to fix ignition problems may be possible on your own, but the process is complex enough to warrant a service call.
  • Large duct leaks. If your ductwork is damaged, heated air can leak into the surrounding spaces, and cold, untreated air can enter the lines. While the furnace may run, enough heated air may not make it to rooms and the system could push cold air into your spaces instead. Large duct leaks can cause drastic heat loss and higher energy bills. Inspect visible ventilation lines for damage and ask a professional to conduct a duct leakage analysis if the problem persists.
  • Clogs in the condensate line. High efficiency condensing furnaces create condensation from combustion gases. If condensate drain lines become clogged, they could cause the system’s pressure switch to open, which could keep your furnace from starting. While this problem may be intermittent, check your drainage pans and drain lines if your system is blowing cold air. If you see a buildup of fluid, check the opening of the tube for clogs and clear it.
  • Dirty air filter. Furnace filters need to be clean to filter air appropriately. Dirty or clogged filters impede airflow, naturally reducing the amount of heated air propelled through ducts into your home. Check your HVAC filters every month, and replace them when they are dirty or as recommended by the manufacturer.
  • Lack of heating fuel. Regardless of whether your furnace relies on natural gas, liquid propane, or heating oil, it requires a set amount of fuel to ignite your furnace. If your fuel reserves are empty or there is a problem with the main supply line, the furnace receives no fuel for heating. Check with your natural gas provider to determine if there has been a disruption in service. Make sure your stored fuel tank is full. You may need to order fuel delivery before you are able to use the furnace again.

6. Air filter clogs quickly

Air filters require routine replacement to work properly. As these screens pull contaminants from the circulating air in your home, they fill with contaminants that block air flow. During winter, filters often need more frequent replacement because of increased heating system use. However, some issues could cause your filter to clog early and need more frequent replacement.  Furnace troubleshooting for this air filter issue may include:

  • Blower fan setting set to “ON”. When your system continuously recirculates air due to the fan being set to “ON,” the filter processes more air, and may become dirty more quickly. Keep your fan set to “AUTO” to help filters last longer.
  • Dirt near air return vents. Air return vents are responsible for sucking air into the system and returning it to your heating unit, where it is filtered and run through the furnace or air handler. Dirt and dust near return vents can introduce more contaminants to filters, clogging them faster. Keep the area around air returns as clean as possible.
  • Heavy indoor pollution. Cooking fumes, cigarette smoke, pet dander, and even overspray from cleaning products can pollute indoor air. High levels of pollutants clog filters faster. High humidity levels due to lack of ventilation can also pollute indoor air, since mold and mildew can grow. Replace air filters frequently if your home smells musty, you smoke indoors, have a large family, take care of indoor pets, or regularly engage in any activity that generates air pollutants, such as woodworking or crafting.
  • Duct damage. Duct leaks and joinery gaps allow outside contaminants, such as insulation particles, to enter your indoor air supply and clog the air filter. Correct duct leaks right away to avoid poor air quality and energy loss, either by patching damaged sections with appropriate foil tape or by professional duct sealing.

7. Thermostat not turning on or appears blank

Your thermostat controls your heating and air conditioning system. If it won’t turn on, it can’t communicate the set temperature to your furnace or heat pump. Here are some reasons your thermostat may look blank or may not turn on.

  • Dead batteries. If your thermostat isn’t hardwired to your home, it uses battery power. If the screen on your thermostat is unresponsive or if the thermostat isn’t switching on the furnace when you move the manual switch, try changing the batteries to your device.
  • Lack of electrical power. If your thermostat is hardwired (wired connection to your home’s electrical system), a problem with your electrical system could be at fault. Older electrical panels may contain fuses that can blow, and you may have one that needs to be replaced. Inconsistent or heavy electrical loads can trip electrical breakers and may prevent the thermostat from powering up. Try resetting the breaker or replacing blown fuses to see if that corrects the issue.
  • Improper settings. Some thermostats can be completely turned off at the source, which makes the screen look blank. If your thermostat has a main power button, try turning the system on. Thermostats should be left on all throughout the year, even if you don’t intend to heat or cool your home at the time.
  • Loose electrical connections. The wiring to your thermostat can be knocked loose by aggressive adjustments, ground movement, or someone accidentally hitting or leaning against the area. Remove the seated thermostat and check for loose wiring. Tighten the screws that connect the wiring. If you see physical damage to either the thermostat or the wiring, have an HVAC technician repair or replace the device or wire.
  • Loose furnace access panel. Some thermostats, especially Honeywell thermostats, are known to shut off altogether when access panels on the furnace are left open. Check your furnace for any panels that are popped out of place, and close them carefully.
  • Tripped float switch. Condensing furnaces typically contain a float switch that is connected to the thermostat. This device is designed to detect high levels of condensation. When the float switch is tripped, power to the thermostat is cut off. Check the condensate drain for moisture accumulation, clear any clogs, and reset the switch if necessary.
  • Heating system overheats. If your thermostat turns blank when you are in the middle of heating your home, it could be a sign that the system has overheated. Overly high temperatures can trigger your furnace’s internal limit switch, halting operations and impacting the thermostat display. Since overheating incidents can be caused by blockages in furnace filters, check your filter to see if it appears dirty and replace it if needed.
  • Malfunctioning thermostat. If your thermostat is unresponsive and you have tried these troubleshooting tips, you may simply need to replace your unit. The average lifespan of a thermostat is about 10 years. New thermostats can be self-installed if you follow the instruction manual closely, but to ensure efficient communication with your heating system, have a trained HVAC professional take care of the job.

8. Furnace creating a burning smell

The first time your furnace runs during the season, it may create a burning smell as it burns off a small amount of dust inside the system. However, if that smell continues past the first few hours of operation, it may be caused by these issues:

  • Dirty air filters. When air filters are filled with dirt and debris, odors often linger. Dirty filters can also allow contaminants to reenter the system, causing the smell to persist. If this is the reason for the smell, replacing the filter will fix the issue.
  • Wiring issues. Problems with your furnace’s internal wiring can cause the insulation to burn or melt, generating a burnt plastic smell. If the odor smells like melting plastic or burning electricity, turn the heating system off and have it inspected by a professional.
  • Overheated motor. When a furnace’s motor overheats, it can generate a burning smell. Oftentimes, overheating is caused by airflow restriction, so check the air filter and vents for blockages. Sometimes, worn motor bearings can cause the system to overheat. If the smell is accompanied by a squealing or grinding noise, bearings could be at fault. Turn off your furnace until you can have it repaired.

9. Water pooling around heating equipment

Conventional furnaces aren’t designed to create condensation as they heat the home. However, condensing furnaces have a second heat exchanger designed to capture more heat from exhaust fumes, giving those gases additional time to cool and become condensate. These high-efficiency furnaces are great for the environment, but condensate leaks cause equipment damage and water damage to the home. Here are a few reasons there may be water pooling around your furnace.

  • Leaking condensate drain (air conditioner). Air conditioners pull moisture out of the air during the cooling process, creating condensation This water is collected in a drainage pan and routed outdoors to a drain. However, if there is water on the floor near your HVAC equipment during the warmer months, it could be a sign that your condensate pan or drain is leaking. While it may look like a furnace issue, try to find the source of the water by listening for drips or checking condensate pans and hoses inside the cabinet. Remove the clog or ask a technician to check for issues.
  • Leaking humidifier component. If you have a whole home humidifier that works alongside your furnace or heat pump, the water supply or drain lines may have a leak which causes water to pool near your HVAC equipment. Check the supply line, drain line, and external casing for damage.
  • Clogged condensate drain (condensing furnace). Condensing furnaces have a drain pump, a tube, and a main drain line that can leak water. Since it can be hard to detect where the water is coming from, schedule a service call to have the components checked, clogs removed, and replacement components installed, if needed.
  • Faulty or improperly installed flue pipe (conventional furnace). Conventional furnaces rely on a flue to move exhaust fumes out of your home. If flue pipes are too long, too large, sloped, damaged, or clogged by debris, gases can stay in place long enough to convert into water. Condensation can leak and pool, creating a puddle. If you notice moisture accumulation around your flue pipe, have the issue inspected and repaired professionally.
  • Cracked secondary heat exchanger (condensing furnace). Cracks in the secondary heat exchanger inside a condensing furnace can allow water to escape and move into the furnace, where it can puddle. Anytime you notice water where it shouldn’t be inside your condensing furnace, report the problem to a professional immediately.

10. Heat pump not warming your home.

Some Cincinnati residents use heat pumps as their primary heating and cooling source all throughout the year. If your heat pump doesn’t seem to generate warmed air, these causes could be to blame:

  • Damaged starting components. If your heat pump does not turn on when expected, the starting capacitor may be bad, causing a slight clicking noise. If this occurs, your heat pump won’t be able to power up, and the capacitor needs to be professionally replaced.
  • Dirty air filter. When filters are dirty, they block airflow. Air filters should be replaced more often during the winter months, so check your every month and replace it when it appears dirty.
  • Refrigerant leaks. Heat pumps rely on refrigerant to move heat from outside to inside during the winter, and from inside to outside during the summer. However, when refrigerant lines leak, your system may not have enough refrigerant to heat your home properly. HVAC technicians inspect and repair damaged refrigerant lines and recharge systems with new refrigerant. It is important to note that only EPA-certified professionals can handle refrigerant, since it can harm the environment.
  • Frigid temperatures. Modern heat pumps offer incredibly energy efficient heating and cooling, but when temperatures become extreme, they can struggle. Heating efficiency can decline whenever the weather is cooler than 25 degrees Fahrenheit. If the weather is too cold, supplemental electric resistance strips or backup gas heating can be added to help.
  • Improper blower fan settings. When blower fans are set to “ON,” your blower fan will run constantly, even if the heat pump isn’t producing heat. Adjust your blower fan to “AUTO” to correct the issue.
  • Improper thermostat settings. Thermostats will not trigger your heat pump to generate warmth if they are set to “COOL” or “OFF.” Check your thermostat to make sure the system is set to “HEAT.”
  • Issues with the reversing valve. Heat pumps rely on a reversing valve to change the system from cool to heat. Unfortunately, if this valve becomes stuck, the system may not heat appropriately. This valve may need to be replaced professionally if the system won’t switch over from cooling to heating.
  • Debris on outdoor unit. Heat pumps extract warmth from the air outside. However, they can’t do this if exterior of the unit covered with leaves, snow, ice, or dirt, blocking air from reaching the refrigerant coils. Clear away debris from the outdoor heat pump unit to see if that fixes the problem.
  • Unit is in the defrost cycle. It’s possible for ice crystals to form on outdoor coils in the winter. Heat pumps use a defrost cycle to warm refrigerant and melt away any ice, which is essentially the unit acting in cooling mode instead of heating mode. If your heat pump isn’t generating warm air, it might not mean that your system is broken at all. Rather, it may just be in the midst of a defrost cycle. Having a supplemental home heating system can help to warm your home during these periods.
  • Iced over heat pump. While heat pumps do contain a defrost system, the system may not be strong enough to melt through heavy ice. Clear any blockages outside that may be leading to heavy ice buildup, such as clogged gutters or fallen snow. If your heat pump ices over easily, have it inspected.

11. Your home has lots of cold spots

If your home feels drafty or you have rooms that always feel cold, your HVAC system may be out of balance. Some parts of your home may receive too much heated air, while others are left frigid. Here are some reasons this may occur.

  • Heating system too small. Undersized heating systems aren’t capable of generating enough heat to warm your home evenly. The only way to correct this cause of cold spots is by adding a supplemental heating source or replace the unit with a properly sized heating system.
  • Heating system too large. Furnaces and heat pumps that are too large for a home can also cause hot and cold spots, as the areas near the unit warm quickly, triggering the thermostat to stop heating – this keeps the rest of the home from being warmed. Proper sizing is essential during HVAC installation, so ask a technician to calculate your home heating load if your system tends to short cycle. Short cycling can also be caused by airflow obstructions or faulty components.
  • Clogged air filters. Dirty furnace filters block airflow. Check your air filter every month, and replace it as recommended by the manufacturer – for standard 1-inch filters, this is typically at least every one to three months.
  • Leaks in your ductwork. When ductwork develops leaks due to physical damage, loose joints, or collapsed runs, airflow into rooms is limited while heated air escapes into places it can’t be used, such as the interior portions of walls or an unfinished attic. Duct leak inspections should be done by a professional and leaks sealed to stop heat loss.
  • Duct blockages. Supply ducts can become blocked when things fall into floor vents, or when furniture or items block air returns. Keep areas around air returns clear and vacuum out the interior component of air vents after removing the register during routine cleaning. Objects that can’t be reached from the vent may need to be professionally removed.
  • Closed room vents. The vents throughout your home should remain open year-round so your HVAC system can work as intended. When vents are closed or blocked by rugs, carpets, furniture, or other household items, they can’t deliver heat to the room. Louvers can be unintentionally closed, so make sure your vents are open and unobstructed to allow heat into the space.
  • Dampers being closed. Some heating systems contain duct dampers to regulate airflow. If dampers are stuck closed, adequate heat won’t be able to enter the room. Check manual dampers to ensure all units are in the proper position. If you have an automatic damper system, a technician may need to test the damper to see if it is responding to thermostat requests appropriately.
  • Uninsulated ductwork. Homes with forced air systems rely on ductwork to deliver warmed air. Unfortunately, when ductwork isn’t insulated, heat loss can occur on its way to the space, lowering the temperature and creating cold spots. Areas farthest away from the furnace are at most at risk for low temperatures. Wrap any exposed ductwork with ventilation insulation or ask a professional to tackle the job.
  • Poor ventilation design. When ducts are too small, airflow is impacted. If ductwork is too large, some areas may receive too much heat. Check with a technician if you suspect that your ductwork is improperly sized.
  • Improper thermostat location. Your thermostat is designed to detect the ambient temperature of a room and respond appropriately. However, if your thermostat is in direct sunlight, near a window, by a door, or inside a confined space like a closet or pantry, it may not respond appropriately. Have a technician move your thermostat if it is in a bad location.
  • Blower fan speeds. Anytime a system uses a multi-speed or variable speed motor, adjustments in speed are sometimes necessary to deliver enough heated air to your home. Check your owner’s manual to see how to adjust your blower fan speeds to improve your comfort or ask your HVAC technician to make the adjustment.
  • Older furnace. Every furnace has a useable lifespan, and some furnaces are simply too old to deliver properly heated air throughout your home. If you have rooms that always feel cold, you may simply need to replace your home heating system.
  • Poor insulation. Inadequate insulation levels also make rooms feel cold, since the heat from warmed air dissipates faster through under insulated walls or ceilings. Make sure your attic has an adequate amount of insulation for your location.
  • Large, multi-level homes. The larger and more complex the floorplan of a home, the more power your heating system needs to properly warm the space. Multi-level homes are prone to cold spots since heat rises and cold air sinks. Zoned heating systems regulate temperatures throughout the space and can be added by a professional.

12. Heating system short cycles

On average, your furnace should cycle for about 10 to 15 minutes each time it starts. If your furnace has a bad habit of starting up and then turning off again after a few minutes or even seconds, it is “short cycling.” Here are a few likely culprits for short cycling.

  • Heating system too large. While having a large heating unit may seem like a solution to a cold home, a system that produces too much warmed air too fast actually causes problems. When the air around the furnace heats up too quickly, it can prompt the thermostat to end the heating cycle early. As your system starts up and shuts down repeatedly, it strains HVAC components, uses extra energy, and results in more frequent breakdowns. Having your furnace replaced is the only solution to the problem.
  • Poor airflow. When dirt and grime fill air filters, airflow is restricted which can strain your furnace or air handler. Your system may overheat, and the internal limit switch may trip. Replace the air filter as soon as it looks dirty.
  • Blocked flue pipe. If the flue pipe that routes fumes from your furnace becomes clogged, your system will turn off to prevent CO2 exposure. Keep flues clear and check them regularly for debris. Always keep a carbon monoxide detector running in your home on every level.
  • Thermostat problems. The thermostat itself can develop problems, especially if it is older, placed in a location prone to stark temperature changes, or dirty or unlevel. Ask a professional to clean, recalibrate, reposition, or replace your unit if it doesn’t appear to be working properly.
  • Incorrect thermostat anticipator calibration. Manual thermostats may have adjustable heat anticipators that increases temperature inside of the thermostat to end a heat cycle early which prevents overheating the space. These older thermostats can be adjusted but may need to be replaced.
  • Faulty flame sensor. Flame sensors inside of furnaces detect when a flame is present. and are designed to shut down your entire system if the flame is out, avoiding explosions and gas leaks. Unfortunately, if these sensors become dirty due to soot, they may shut down the system early for safety. These sensors can be cleaned or replaced by a professional if they are the cause of the problem.
  • Damaged furnace draft inducer motor. Some furnaces have a draft inducer motor that is designed to expel combustion gases leftover after a heating cycle. If the air pressure switch doesn’t detect enough airflow, it may shut down the furnace. To prevent this problem, keep your flue pipes free of debris. If the issue persists, there may be a fault in the pressure switch or draft inducer motor.

13. Furnace or air handler interior visibly dirty

When you open up your furnace or air handler access panels, is the interior extra dirty? Sometimes, a buildup of dust and grime can be an indicator of these issues:

  • Air filter issues. Dirty air filters allow grime to pass into the system. Accumulations can damage efficiency, driving up utility costs. To avoid problems, change your air filters as soon as they look dirty, and schedule routine heating maintenance before each winter.
  • Cracked heat exchanger. When the heat exchanger inside your furnace cracks, it can allow soot from your furnace’s exhaust system to escape to other areas of the appliance. If you notice soot inside the system, have your furnace inspected and repaired immediately. Cracked heat exchangers can leak carbon monoxide and need to be professionally replaced.
  • Carbon accumulations on burners. If carbon builds on your furnace burners, the interior of your furnace will appear dirty. Additionally, soot can cause incomplete fuel combustion, triggering a yellow flame instead of the healthy, blue flame you should see inside your furnace. Burners can be carefully cleaned by following the instructions detailed inside your furnace owner’s manual, or you can have them professionally maintained.

14. Excess humidity in your home

Folks from Cincinnati are used to higher humidity levels in the summer, but since cold air isn’t as capable of holding onto moisture, winters are typically drier. However, when humidity levels at home cause issues like fogged windows and condensation, you may also find yourself struggling with mold or mildew damage. Here are a few HVAC issues that could cause extra moisture inside your home.

  • Humidifier trouble. Since winters can be so much drier than the rest of the year, some families use whole house humidifiers to make their homes more comfortable. However, if your humidifier isn’t working properly, extra humidity may be released into the air, and you may struggle with moisture accumulation.
  • Inadequate ventilation. Ventilation and is designed to move fresh, outdoor air into your home and move out moist, stale indoor air. If your home HVAC system is not designed with enough ventilation, moisture concerns can pop up indoors. Ask a professional to assess the ventilation in your home if you feel like your air sits stagnant.
  • Missing exhaust fans. Exhaust fans and fume hoods are designed to move indoor pollutants like cooking fumes and bad odors outside, as well as moisture. If your home does not have exhaust fans, or they are not working properly, your home may be more humid. HVAC contractors can install added exhaust fans, helping you to control indoor humidity.

15. Your heating bills are high.

Utility costs can vary from month to month, but when your heating bills are much higher than previous years, air leaks and heating system issues could be at fault. Here are a few reasons your HVAC equipment may be costing more to run this year than normal:

  • Grimy air filters. Air filters are designed to trap particulates, but when they become laden with dirt and microscopic debris, air can’t pass through easily, and the system works harder. Check your air filters at least every month during high-use periods like winter, and replace them when they look dirty.
  • Incorrect thermostat programming. Programmable thermostats make it easy to set your system to heat or cool efficiently. However, if the date, time, or settings are incorrect, you could be heating your home more often than you might like, which can drive up energy costs. Make sure your thermostat is set appropriately, and that the fan is set to “AUTO.”
  • Short cycling furnace. If your furnace switches on, runs for a few minutes, and then turns off, it is short cycling, which is very inefficient and expensive. Short cycling can be caused by obstructions in the flue, improperly sized HVAC equipment, and dirty filters. If replacing the filter does not correct the issue, ask a professional to inspect your system.
  • Ductwork insulation issues. Ductwork in basements, attics, and exterior walls can become quite cold, especially on a chilly winter’s night. As heated air travels through cold lines, it can lose heat. Prevent this problem by insulating your ductwork carefully, especially ducts near the exterior of the home.
  • Ductwork leaks. In the United States, the average home loses up to 30% of its heated air through ductwork leaks. Lost heat increases energy costs as the heating system works to replace it, so make sure your ductwork is installed properly, sealed, and inspected by a professional.
  • Using a heat pump in bitterly cold weather. While air source heat pumps are designed to be very efficient when temperatures are above freezing, lower temperatures can drastically reduce the efficiency of some models and increase energy costs. Consider having a secondary heating system installed, such as a forced air furnace. You could also have a cold climate heat pump
  • Using supplemental heating systems. While supplemental heating systems (also referred to as emergency or auxiliary heat) can keep your home warmer, they can increase energy costs. Only use these additional heating systems when outdoor temperatures are below freezing and you use a heat pump, the system is in the middle of a defrost cycle, or if there are issues with your heat pump. Check to ensure that your heat pump is in “HEAT” mode instead of “EMERGENCY HEAT” mode.
  • Old, inefficient heating equipment. New, efficient heat pumps and furnaces are designed to convert more energy to heat, reducing your energy costs. Updating your furnace can help you to save a significant amount of money, since older systems have an efficiency between 56% and 70% AFUE, some modern systems are nearly 100% efficient.

16. Carbon monoxide detectors sound frequently

Every home with a gas furnace should have carbon monoxide detectors on every level, since the combustion that takes place in the engine can generate this colorless, odorless, toxic gas. If CO2 detectors sense that the gas is present, they will sound an alarm to alert homeowners to seek fresh air. Here are a few reasons your furnace may be emitting dangerous carbon monoxide.

  • Installation mistakes. Furnace flues are designed to move dangerous gases, like CO2, out of your home. However, if the flue wasn’t installed properly, it may allow CO2 to collect inside the pipe and leak into your home. To keep this from happening, you should never install a furnace on your own. If you suspect issues with your flue, work with a trusted HVAC contractor to repair or replace the pipe.
  • Damaged or blocked flue pipe. Combustion exhaust gases are supposed to safely exit the home through the flue of a conventional furnace. If the flue pipe is blocked or damaged, these gases may back up into the home. Inspect the pipe for damage, rust, and corrosion. Check the roof exit or exit on the outside wall of the house near where the furnace is located indoors – animal nests, ice, and other debris can cause clogs. Always leave a minimum of five feet open around the flue pipe.
  • Back drafting. Backdrafts can happen when air is drawn out from the combustion chambers or the exhaust instead of pushing air through this area, allowing CO2 to enter the home’s air supply. This issue can be caused by depressurization inside the heating system or ducts. To repair this issue, professionals may need to carefully inspect and test your furnace to diagnose the cause of the problem.
  • Heat exchanger cracks. The heat exchanger heats air flowing over it, using heat from combustion gases held inside. Unfortunately, if the exchanger cracks, it can allow CO2 generated through combustion to enter into your circulated home air. Exchanger cracks are commonly caused by neglect, damage, rust, or corrosion, which can be prevented through regular professional maintenance.

17. Noisy heating system

When your furnace or heat pump system runs, it should make some gentle, blowing operating noise, but nothing irregular or severe. If your furnace or heat pump louder than normal or you notice new sounds, here are some potential causes:

  • Loose panel. If your furnace or air handler cabinet has access panels that have popped out of place due to a missing screw or improper replacement, it could cause the entire system to rattle slightly as it moves. Make sure all panels are sitting flush with the flat plane of that side of the cabinet and replace any missing screws.
  • Motor bearing issues. Unlubricated motor bearings can create a grinding noise when your furnace runs. Bearings should be oiled every year to avoid wear and tear.
  • Fan belt problems. A belt inside your furnace or air handler connects the fan and motor. If your system emits a squealing sound, tighten or replace the belt
  • Delayed ignition. Sounds that only occur when the furnace starts could indicate delayed ignition issues. When ignition systems don’t burn fuel appropriately, they can emit a loud bang. Professional technicians can inspect the ignition system and make repairs.

18. Your furnace needs more repairs than normal.

While it is normal for a homeowner to seek occasional repairs for their HVAC system, a furnace or heat pump that needs many repairs during a single season spells trouble. Here are a few reasons your heating unit may need many repairs.

  • Inadequate maintenance. Routine professional maintenance includes services like deep cleanings, lubrication, and fine tuning of components. However, if these maintenance visits are skipped, your system could malfunction without warning. Tune ups are needed every year, ideally before winter.
  • Obsolete system. On average, gas furnaces last 15 to 20 years, and heat pumps typically last 12. System breakdowns and repairs are most common in the last two years of a system’s functional lifespan. If you have called for service recently and you find yourself seeking help again, it may be a clear sign you should seek a replacement. Some modern HVAC systems even track performance and issue alerts when service or replacement is needed, so pay attention to your system. Read your furnace’s owner’s manual to make sure you are familiar with what alerts mean, and how they should be addressed.

19. Furnace stays on.

If your furnace or heat pump seems like runs constantly, it could be caused by one of these issues:

  • Damaged thermostat. Thermostats typically last about ten years before replacement is needed. If your thermostat doesn’t seem to correctly communicate with your heating equipment, check to see if the wiring inside the seated unit is secure. If you find loose wires, tighten them. If the internal portion of the thermostat appears damaged, replace the unit.
  • Stuck limit switch. Furnaces contain a limit switch that monitors the temperature inside the unit and cuts the power if the temperature gets too high. If the limit switch is stuck, the blower may stay on. The limit switch may be reset to solve the issue, or replacement may be necessary.
  • Improper fan settings. If your blower motor is set to “ON,” your system may emit air continuously from air vents. While you may worry that your system is heating around the clock, it’s only the blower motor emitting unheated air. Always keep your system set to “AUTO” to ensure the blower only operates when a heating cycle is in session.
  • Faulty compressor contractor. When a heat pump has a compressor contractor that isn’t operating correctly, the electricity to the pump is not correctly regulated. The system could have constant power and run non-stop. Damaged compressor contractors should be professionally replaced.

20. Thermostat displays a service message.

Some smart thermostats are designed to monitor and track heating system performance and show alerts when issues are present. However, thermostat notifications are highly specific and vary from model to model, so become familiar with your system. Learn which kinds of alerts your system is capable of generating, such as filter replacement reminders, trends in operation, efficiency issues, or temperature control problems. Anytime you receive an error code or alert you are unfamiliar with, refer to your owner’s manual or the manufacturer’s website.

Avoiding Common Heating Problems

While some heating issues are inevitable, many are caused by ongoing maintenance issues. For these reasons, ongoing maintenance is necessary to keep your furnace or heat pump in excellent working condition.

Routine professional maintenance provides opportunities to spot damage and counteract wear and tear which works to prevent breakdowns. Furnaces need a single tune up every year, while heat pumps require two annual tune ups, since they operate as both heating and cooling systems. Schedule a maintenance call every spring and fall to keep your system in great shape.

Thomas & Galbraith Heating, Cooling & Plumbing Is Here To Help

Anytime you experience trouble with your furnace or heat pump, the team at Thomas & Galbraith Heating, Cooling & Plumbing is here to help. Our team of NATE-certified HVAC technicians help with everything from preventative maintenance to emergency repairs to keep your home safe and comfortable. Schedule your heating tune-up today to ensure your home stays cozy all winter long.

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