furnace repair

What to do When Your Furnace Will Not Switch On

It might seem scary to troubleshoot your furnace when your heat won’t turn on. 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 many of these fixes are fast and affordable (or even free).

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

When you need a pro in Wharton, Faust Air Conditioning and Heating can help.

We service most makes and models of furnaces. If you need a more modern heating system, we also offer furnace replacement and furnace installation.

Furnace breakdowns are usually caused by a lack of routine maintenance. These checkups often reveal a costly problem before it begins—and causes your HVAC system to stop working.

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

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 a new thermostat.
  • Confirm that the switch is set to “heat” instead of “off” or “cool.”
  • Find out if the program is displaying the current day and time and is set to “run.” If you can’t change the program, change the temperature by pushing the up/down arrows and press the “hold” button. This will require the furnace to turn 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 fairly quickly. If it doesn’t, see if it has power by pushing the fan switch from “auto” to “on.” If the fan doesn’t start instantly, your furnace may not be connected to power.

If you’re connected to a Wi-Fi thermostat—like one made by Nest, Ecobee, Lux, Honeywell or Bosch—check the manufacturer’s website for help. If you can’t get your smart thermostat to turn on, call us at 979-532-2511 for assistance.

Smart Thermostat

Check Breakers and Switches

If you’ve already checked your thermostat, you will want to make sure your breakers and furnace switch are on.

  • Go to 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.
  • Pinpoint 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 shift the breaker to the “on” position. If the breaker trips and pops back to “off” after you do this, leave it alone. Contact an expert from Faust Air Conditioning and Heating at 979-532-2511 immediately.

Your furnace has at least one wall switch placed on or near it—no matter when it was made or who manufactured it.

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

Replace Your Air Filter

Dirty, blocked air filters often cause complications that are easily avoidable.

  • Your furnace can overheat and stop working too soon, due to dust in the filter restricting 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 excessively 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 position depends upon what type of furnace you have.

Replace furnace filter

When switching out your filter:

  • Turn off your furnace completely.
  • Pull out 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.
  • Replace the new filter with the arrow pointing toward the furnace to avoid damaging your system.

To make the process easier next time, use a permanent marker on your furnace housing or ductwork to indicate the airflow direction and filter size.

We recommend replacing flat filters each month. Pleated filters usually last about three months. You can also get a washable filter that will work for about 10 years.

If you have children or pets, you may need to change your filter more often.

Look at Your Condensate Pan

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

Follow these steps if your furnace is dripping 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: Find the float switch. If the switch is “up” and there’s water in the pan, call us at 979-532-2511. You will most likely need a new pump.

Peek Inside Your Furnace

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

Call us at 979-532-2511 if you see anything other than a solid, colored light or blinking green light. Your furnace is probably giving an error code that requires professional help.

Clean Your Flame Sensor

Is your furnace trying to start but turning off without blowing heat? A dirty flame sensor could be at fault. 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 comfortable opening up your furnace. We can also do it for you.

Hoping to tackle 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 track 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 regularly. If it doesn’t turn on, the sensor might need to be updated. Or something else could be the issue. Call us at 979-532-2511 for help if this happens.

Relight the Pilot Light

If your furnace is an older model, its pilot light could be 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.
  • Switch the knob to “pilot.”
  • Hold down the “reset” button as you deliver the flame of a long lighter to the pilot light opening.
  • Release the “reset” button once the pilot light is lit.

Contact us at 979-532-2511 if you’ve followed the guide twice and the pilot won’t light or stay lit.

Check Your Fuel Source

Are other gas appliances functioning? 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 start?

Call us today at 979-532-2511 or use our online scheduler. We’ll come out to your home and identify what’s wrong.

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