furnace repair

What to do When Your Furnace Will Not Switch On

It might feel scary to troubleshoot your furnace when your heat won’t work. But it doesn’t have to be that way.

You might be able to bypass a furnace repair call with our DIY troubleshooting guide. You don’t need any technical skills. And most of these fixes are fast and inexpensive (or even free).

This list will walk you through how to fix your furnace when it won’t turn on, won’t stay on or won’t light.

When you have to have a pro in Ballwin, Air Alliance Team can lend a hand.

We repair and maintain most makes and models of furnaces. If you need an updated heating system, we also offer furnace replacement and furnace installation.

Furnace breakdowns are generally caused by forgotten routine maintenance. These service appointments often highlight a costly problem before it gets worse—and causes your HVAC system to break down.

During this service, our NATE-certified professionals will thoroughly inspect your furnace, make sure it’s operating properly and lubricate moving parts. A well-managed furnace often lasts longer and operates more efficiently, saving you more on your heating charges.

Ready to begin troubleshooting your furnace? Follow our step-by-step guide below.

Steps for Troubleshooting Your Furnace

Inspect Your Thermostat

Start by looking at your thermostat. Is it telling your furnace to start?

If you have a digital thermostat:

  • Change the batteries if the screen is blank. If the digital screen is scrambled, you may need to replace your thermostat.
  • Confirm that the switch is set to “heat” instead of “off” or “cool.”
  • Look to see if the program is showing the current day and time and is set to “run.” If you can’t change the program, set the temperature by pushing the up/down arrows and press the “hold” button. This will require the furnace to switch on if thermostat programming is causing an issue.
  • Set the temp to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should turn on shortly. If it doesn’t, double check that it has power by sliding the fan switch from “auto” to “on.” If the fan doesn’t start right away, your furnace may not have access to power.

If you’re connected to a Wi-Fi thermostat—like one made by Nest, Ecobee, Lux, Honeywell or Bosch—refer to the manufacturer’s website for guidelines. If you can’t get your smart thermostat to function properly, call us at 636-206-4250 for assistance.

Smart Thermostat

Check Breakers and Switches

After that, you will have to make sure your breakers and furnace switch are on.

  • Find your house’s main electrical panel. It’s the gray metal box on the wall in your basement, garage or closet.
  • Dry off your hands and feet before working with the panel or breakers.
  • Find the breaker labeled “furnace” or “heat” and make sure that it’s switched in the “on” position. If the breaker has tripped, it will be in the middle or “off” position.
  • With one hand, firmly push the breaker to the “on” position. If the breaker trips and moves back to “off” after you do this, leave it alone. Contact a technician from Air Alliance Team at 636-206-4250 as soon as possible.

Your furnace has at least one wall switch located on or near it—no matter its age or brand.

  • This switch should be flipped up in the “on” position. It can take your furnace up to five minutes to start if the switch was off. (Not sure where your furnace is? Look in your basement, garage or utility closet. It could also be located in a crawl space or attic.)

Replace Your Air Filter

Dirty, clogged air filters often create issues that are easily avoidable.

  • Your furnace can overheat and stop working too soon, due to dust in the filter hampering airflow.
  • Your energy bills could get more expensive, because your furnace is starting up more often.
  • Your furnace may not last as long, because it has to work harder.
  • Your furnace could lose power, because an extra dirty filter can cue the breaker to trip.

You can find your air filter inside your furnace’s blower component, attached filter case or wall-mounted return air grille. Its placement depends upon what type of furnace you have.

Replace furnace filter

When switching out your filter:

  • Shut off your furnace completely.
  • Grab the filter, hold it up to the light and look through it. Place a new filter in your system if you can’t see light through it.
  • Put in the new filter with the arrow pointing toward the furnace to avoid damage.

To make the process simpler for yourself, use a permanent marker on your furnace housing or ductwork to indicate the airflow direction and filter size.

We suggest replacing flat filters monthly. Pleated filters generally last about three months. You can also get a washable filter that will last about 10 years.

If you have children or pets, you may need to switch out your filter more frequently.

Check Out Your Condensate Pan

Condensate pans, or drain pans, capture water your furnace takes from the air.

Follow these steps if your furnace is seeping water or there’s standing water in the pan.

  • If your pan has a PVC pipe/drain: Be sure that it’s not blocked. If it’s not, you can use a special pan-cleaning tablet from a home improvement or hardware store.
  • If your pan has a pump: Check out the float switch. If the switch is “up” and there’s water in the pan, call us at 636-206-4250. You will probably need a more modern pump.

Check Inside Your Furnace

You can check the status of your furnace’s blower motor by checking inside the plastic window. Depending on the type, this light could be located on the outside of your furnace.

Call us at 636-206-4250 if you see anything other than a solid, colored light or blinking green light. Your furnace could be giving an error code that needs professional assistance.

Clean Your Flame Sensor

Is your furnace making an effort to start but shutting down without producing heat? A filthy flame sensor could be be the reason. When this happens, your furnace will try to turn on three times. Then, a safety feature will shut it down for about an hour.

You can clean the flame sensor yourself if you feel alright opening up your furnace. We can also do it for you.

Hoping to take on cleaning the sensor yourself? You’ll need the following:

  • A 1/4” hex screwdriver or wrench
  • Piece of light-grit sandpaper, steel wool or emery cloth
  • A dry, clean paper towel

Next:

  • Use your furnace’s wall switch or breaker to shut off the power. Shut off the gas too if your gas valve is not electric.
  • Remove your furnace’s front panel and trace the wire to the flame sensor, which looks like a thin, bent rod.
  • Unscrew the rod and use your sandpaper, steel wool or emery cloth to gently clean the metal rod.
  • Use a paper towel to wipe off the rod.
  • Replace the sensor.
  • Put your furnace’s doors back on.
  • Turn the furnace’s power back on. Your furnace may run through a series of checks before it starts normally. If it doesn’t kick on, the sensor might need to be switched out for a new one. Or something else could be wrong. Call us at 636-206-4250 for guidance if this happens.

Relight the Pilot Light

If your furnace is an older style, its pilot light could be blown out. Relight it following the instructions on the label. You can locate the label on your furnace’s doors.

Or you can follow these steps:

  • Locate the switch on the bottom of your furnace labeled “pilot,” “on” and “off.”
  • Rotate the switch to the “off” position.
  • Wait at least five minutes. This avoids the possibility of starting a fire.
  • Turn the knob to “pilot.”
  • Hold down the “reset” button as you deliver the flame of a long lighter to the pilot light opening.
  • Stop holding the “reset” button once the pilot light is lit.

Contact us at 636-206-4250 if you’ve followed the steps twice and the pilot won’t light or stay lit.

Check Your Fuel Source

Are other gas appliances working? If they’re not, your natural gas service could be off. Or you could be out of propane.

We Can Diagnose Furnace Problems

Made it through our troubleshooting guide but your furnace still won’t turn on?

Call us today at 636-206-4250 or use our online scheduler. We’ll come out to your home and identify what’s wrong.

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