furnace repair

What to do When Your Furnace Wont Switch On

It might feel overwhelming 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 skip a furnace repair call with our DIY troubleshooting guide. You don’t need any mechanical skills. And the majority of these fixes are brief and inexpensive (or even free).

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

When you need a pro in Opelika, Farnell Mechanical, Inc. can be there.

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

Furnace breakdowns are often caused by neglected routine maintenance. These evaluations often reveal a high-cost problem before it begins—and causes your HVAC system to fail.

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

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

Steps for Troubleshooting Your Furnace

Inspect Your Thermostat

Start by examining 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.
  • See if that the switch is set to “heat” instead of “off” or “cool.”
  • Make sure the program is displaying the right 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 force the furnace to start if thermostat programming is causing a problem.
  • Set the temperature to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should kick on within a few minutes. If it doesn’t, make sure it has power by sliding the fan switch from “auto” to “on.” If the fan doesn’t run right away, your furnace may not have 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 work, call us at 334-245-4748 for support.

Smart Thermostat

Check Breakers and Switches

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

  • Head 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 handling the panel or breakers.
  • Locate the breaker labeled “furnace” or “heat” and double-check that it’s switched in the “on” position. If the breaker has tripped, it will be in the center or “off” position.
  • With one hand, firmly move the breaker to the “on” position. If the breaker trips and goes back to “off” after you do this, leave it alone. Contact an expert from Farnell Mechanical, Inc. at 334-245-4748 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 start if the switch was off. (Not sure where to find your furnace? Look in your basement, garage or utility closet. It could also be placed 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 turn off too soon, due to dust in the filter diminishing airflow.
  • Your energy bills could increase, because your furnace is turning on more often.
  • Your furnace may have a shorter life span, because it has to work harder.
  • Your furnace could lose power, because a very dirty filter can cause the breaker to trip.

You can get to your air filter inside your furnace’s blower component, attached filter case or wall-mounted return air grille. Its placement depends upon what kind 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. Replace it if you can’t see light through it.
  • Install the new filter with the arrow pointing toward the furnace to avoid damaging your system.

To make the process less difficult in the future, 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 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 often.

Inspect Your Condensate Pan

Condensate pans, or drain pans, catch 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: Check 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 water in the pan, call us at 334-245-4748. You will probably need a new pump.

Look Inside Your Furnace

You can check the condition 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.

Contact us at 334-245-4748 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 service.

Clean Your Flame Sensor

Is your furnace making an effort to start but shutting off without generating heat? A soiled 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.

Hoping 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 turn off the power. Shut off the gas too if your gas valve is not electric.
  • Open 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.
  • Put back 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 start, the sensor might need to be updated. Or something else could be wrong. Call us at 334-245-4748 for guidance if this happens.

Relight the Pilot Light

If your furnace is an older design, its pilot light could be out. Relight it following the instructions on the label. You can find 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 move the flame of a long lighter to the pilot light opening.
  • Release the “reset” button once the pilot light is lit.

Call us at 334-245-4748 if you’ve followed the instructions 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 work?

Call us today at 334-245-4748 or use our online scheduler. We’ll come out to your home and figure out what’s wrong.

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