furnace repair

What to do When Your Furnace Refuses to Switch On

It might appear stressful to troubleshoot your furnace when your heat won’t turn on. But it doesn’t have to be that way.

You could be able to skip a furnace repair call with our DIY troubleshooting guide. You don’t need any technical skills. And the majority of these fixes are quick and low-cost (or even free).

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

When you require a pro in Saint Peters, C-N-O Comfort Zone can be there.

We service 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 checkups often highlight an expensive problem before it begins—and causes your HVAC system to fail.

During our visit, our NATE-certified professionals will thoroughly inspect your furnace, make sure it’s functioning properly and lubricate moving parts. A well-maintained furnace often lasts longer and operates more efficiently, saving you more on your heating costs.

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

Steps for Troubleshooting Your Furnace

Check Your Thermostat

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

If you have a digital thermostat:

  • Replace the batteries if the screen is off. If the digital screen is scrambled, you may need to replace your thermostat.
  • See if that the switch is set to “heat” instead of “off” or “cool.”
  • Make sure the program is presenting 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 compel the furnace to start if thermostat programming is causing complications.
  • Set the thermostat to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should kick on shortly. If it doesn’t, see if it has power by sliding the fan switch from “auto” to “on.” If the fan doesn’t work immediately, your furnace may not have access to power.

If you’re using a Wi-Fi thermostat—like one made by Nest, Ecobee, Lux, Honeywell or Bosch—turn to the manufacturer’s website for advice. If you can’t get your smart thermostat to turn on, call us at 636-255-8997 for support.

Smart Thermostat

Check Breakers and Switches

Next, you will need 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.
  • Pinpoint the breaker labeled “furnace” or “heat” and confirm that it’s switched in the “on” position. If the breaker has tripped, it will be in the midpoint or “off” position.
  • With one hand, firmly push 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 C-N-O Comfort Zone at 636-255-8997 immediately.

Your furnace has at least one wall switch situated 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 kick on 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, clogged air filters often cause issues 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 climb, because your furnace is working more often.
  • Your furnace may fail permantly faster, because it has to work harder.
  • Your furnace could lose power, because a very dirty filter can prompt 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 location depends upon what model of furnace you have.

Replace furnace filter

When changing out your filter:

  • Turn off your furnace completely.
  • Pick up the filter, hold it up to the light and look through it. Replace it if you can’t see light through it.
  • Install the new filter with the arrow pointing toward the furnace to avoid damage.

To make the process simpler next time, 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 be good for about 10 years.

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

Inspect Your Condensate Pan

Condensate pans, or drain pans, hold water your furnace takes 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 open. 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: Take a look at the float switch. If the switch is “up” and there’s liquid in the pan, call us at 636-255-8997. You will most likely need an updated pump.

Check Inside Your Furnace

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

Reach out to us at 636-255-8997 if you see anything other than a steady, colored light or blinking green light. Your furnace is probably giving an error code that requires professional assistance.

Clean Your Flame Sensor

Is your furnace attempting to start but shutting down without generating heat? A dirty flame sensor could be at fault. When this occurs, 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.

Ready to try 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 as usual. If it doesn’t kick on, the sensor might need to be replaced. Or something else could be wrong. Call us at 636-255-8997 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.
  • Switch the knob to “pilot.”
  • Hold down the “reset” button as you move the flame of a long lighter to the pilot light opening.
  • Let go of the “reset” button once the pilot light is lit.

Reach out to us at 636-255-8997 if you’ve followed the guide twice and the pilot won’t light or stay lit.

Check Your Fuel Source

Are other gas appliances operating? 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 636-255-8997 or use our online scheduler. We’ll come out to your home and identify what’s wrong.

*Required fields