What Should You Do if Your Furnace Doesn't Turn On?

As soon as you realize that your heating system won’t turn on, you may be worried that you are due for a replacement. Many homeowners are apprehensive to do any troubleshooting when it comes to their air conditioning or furnace, since blower motors, heat exchangers, electrical circuits, and gas valves can seem difficult to check or repair. However, when you are armed with the right information, you may be able to see the source of the problem before you call in the help of a professional HVAC technician.

Use this guide to learn what you need to do when your heat isn’t working properly. These simple, step-by-step instructions can help you to identify and repair issues quickly, so you can ensure that your home stays comfortable and safe. Remember, anytime you need service, you can call us here at Thomas & Galbraith Heating, Cooling & Plumbing.

1. Thermostat Not Powering Up

Your thermostat needs a power source to relay electrical information to your HVAC equipment. Some thermostats are hardwired, which means they are connected directly to your home’s power mainframe with wiring. Others rely on batteries to receive the power they need to run your system. Even hardwired thermostats may have battery backups, so they don’t lose full functionality during a power outage. Check these things to make sure your thermostat is receiving power.

  1. Display: Look at your thermostat carefully. Does the unit have any lights on, or any text displayed on the screen? If the screen is completely blank, it may signal a lack of power.
  2. Battery Status: Find the battery compartment within the thermostat and replace the batteries. If the batteries look corroded or you can tell they are old, your system may require battery power to function properly. Replace the batteries to see if power is restored. If your unit is hardwired, check the breaker panel for tripped breakers, and reset any that are out of place.

2. Thermostat Set Incorrectly

Incorrect thermostat settings can spell trouble with your furnace. While it may seem like your heater simply isn’t turning on because of a problem, a simple issue with a date, time, setting, or switch can render your system unresponsive. Check these settings on your thermostat to ensure proper heating.

  1. Date and Time: Make sure that the date and time are accurately reflected in the readings on your thermostat. Check to see if the “AM” and “PM” settings are appropriate for the current time.
  2. Heat Mode: Check to see if your thermostat is in “HEAT” mode. Sometimes, units are accidentally switched to “COOL” or “HOLD,” which can interrupt with normal heating. You should also check that the temperature setting is a few degrees higher than the current room temperature, so you can see if a heating cycle is triggered.
  3. Hold Setting: Whether you are home and need more heat or you are headed to the store and don’t want to heat an empty home, use the “HOLD” setting appropriately. Use the “HOLD” setting when you need to make occasional adjustments to the normally scheduled thermostat temperatures and make sure to turn it off when you are finished.

3. Furnace Not Powering On

Furnaces require fuel to operate. Gas furnaces require both a natural gas source and an electrical connection to run, while electric furnaces only require power. If your system isn’t receiving the power it needs, it will not power on and work to heat your home. Here are some things to check if your furnace isn’t powering on.

  1. Breaker boxes: Find the breaker box in your home and open the panel. Find the breaker that controls the furnace and see if the paddle has tripped. If it has tripped, it may be very slightly out of place. If this is the case, flip it one direction and flip it the other to reset it.
  2. Power switches: Furnaces also contain a physical on/off switch near each unit. Check these switches to see if they have accidentally been flipped.
  3. Internal fuses: Furnaces contain a control panel with internal fuses. These fuses track the power levels running through your furnace and are designed to break if the system’s electrical amperage is off. However, blown fuses will render your furnace inoperable, and they can become blown for simple reasons, such as a power surge after a storm, or forgetting to turn off power before switching out a thermostat. Here are a few steps for checking furnace fuses.

    1. Switch off power to your furnace using the breaker.
    2. Open the furnace access door, which should show you the circuit board. Find the fuse. Fuses are often colored, small, and plastic.
    3. Take the fuse out of the panel and inspect it with a flashlight. Burned out fuses should be burnt or broken internally.
    4. Bring the fuse with you to the hardware store to find an identical replacement. Replace the fuse by firmly pressing the new fuse into place.
    5. Close the panel and restore power to the furnace. Adjust the thermostat to a temperature a few degrees higher than the ambient temperature to see if the system turns on.
    6. If the furnace operates properly the fuse was likely the problem. If the fuse blows again quickly, there may be more complex electrical problems inside your furnace. If the fuse continues to blow and the furnace still isn’t working, there may be a deeper electrical problem at fault inside your furnace. Place a service call to have the electrical connections tested and repaired.
  4. Gas valves: Natural gas furnaces use gas to fuel the combustion sequence inside your furnace that generates heat. If your system isn’t powering on, the valve may be closed. Near your furnace, there should be a gas line with a valve. The valve should be open, or turned to sit in line with the gas line, if it is open. If the valve is closed, it may be sitting perpendicular to the line. Open the valve to run in line with the pipe if it is closed.

If the valve is open, but your system isn’t powering up, there may be a natural gas disruption in your area. Contact your utility company to ask if that is the case. If there aren’t gas disruptions, there may be problems with your system that are triggering safety switches to trip, such as problems with your pressure switch, draft inducer motor, or circuit board. Contact a professional to inspect your system for worn or damaged components, and make the necessary repairs.

4. Furnace Access Panels Open

To protect homeowners, most furnaces have a built-in safety feature that prevents the system from operating if access panels are not properly in place. Check your furnace for any panels that are missing screws, popped out of place, or open for any reason. Replace them and secure the panels to see if that resolves the issue.

5. If Your Furnace Does Not Ignite

When your furnace switches on but the air blowing into your house isn’t warm, it may mean that your system isn’t igniting and producing the flames necessary to generate heat. Here are a few things you should check if you suspect your furnace isn’t igniting appropriately.

Pilot Light Not Burning

Most older furnaces use pilot light ignitions, which are a steadily burning flame that ignites the furnace when the system starts up. However, if the pilot light goes out, it could mean your furnace is incapable of heating your home. Many homeowners assume they would smell natural gas if their pilot went out. However, furnaces typically have a failsafe that halts the flow of natural gas if the pilot goes out. Follow these steps to relight your pilot light.

  1. Unscrew the access panel that covers your furnace and pilot light assembly. Find the reset switch, and turn it to the off position.
  2. Give your system 5-10 minutes before you start. This gives any lingering natural gas the chance to dissipate.
  3. Turn the switch to the “PILOT” setting to give natural gas the chance to flow. Hold in the reset switch with one hand, while you use your other hand to light the pilot with a match or lighter. Hold in the switch until the light burns steadily.
  4. Release the switch, and continue to monitor the pilot light. If the flame flickers or goes out, you need to call for repairs.

Dusty Electric Ignition

Anytime appliances burn fuel to produce heat or power, soot can build up within the system. Newer furnaces that use electronic ignitions an develop dirt and dust buildups inside the system, which stops the ignition sequence from starting the system. When this happens, the furnace can emit a clicking noise, which signals the fact that the furnace is trying to turn back on but is unable to complete the ignition sequence. Cleaning the ignition can help but be exceptionally careful. The ignition components are delicate and can be damaged easily. If they become damaged, the ignition will need to be replaced.

  1. Turn off the breaker that controls your furnace or use the “ON/OFF” switches on the side of your furnace to cut the power.
  2. Turn off the natural gas lines. To close this valve, turn it perpendicular to the supply line.
  3. Open the access panel that sits in front of your furnace’s burner chamber.
  4. Locate the ignitors. They look like ceramic components with electrical connections at the end. Use canned air to dust off the ignitors. Try to dust off these components from a distance of at least a foot.
  5. Replace the access panel and restore power to your furnace. Open the gas valve. If your furnace turns on and operates normally, you may have fixed the issue. If it doesn’t, the ignition may need to be replaced.

6. Furnace Short-Cycling

If your furnace turns on, but then turns off quickly, it may be “short cycling.” This happens sometimes when there are airflow problems or buildups of dust and grime within the furnace body. Here are a few reasons your heater can short cycle.

Air Filter Clogs

Dirty air filters can keep cool air from traveling into your furnace to be heated, which can cause a buildup of heat within the heater itself. These high temperatures can cause your furnace to shut down to protect the inner workings of the system. Check furnace filters regularly and replace them as soon as they appear dirty.

Grimy Flame Sensor

Furnace flame sensors are made to detect the presence of a flame as gas flows through your system. If these sensors become dirty because of soot, they may not sense the flame and could shut down your furnace. Here are a few steps for cleaning the flame sensor if it becomes dirty.

  1. Switch off the power to the furnace. Turn off the gas valve.
  2. Unscrew and remove the access panel.
  3. Locate the flame sensor and remove it. This component can be removed by using a ¼ inch hex wrench. Slide the unit out. In some instances, you may need to remove a wire to access this unit better.
  4. Using very, very fine sandpaper, rub the flame sensor rod to whisk away soot and carbon buildup.
  5. Wipe the sensor down with a clean cloth.
  6. Reconnect the wire and reattach the flame sensor.
  7. Replace the access panel and restore gas and power to your furnace.

When to Call for Professional Repair

Remember, you are never alone when it comes to your HVAC system. Our team is always on standby for urgent troubleshooting and help, and we can come out to help any time of day or night. Here at Thomas & Galbraith Heating, Cooling & Plumbing, we are committed to keeping our customers safe and comfortable through efficient and proactive repairs.

Related Reading