furnace repair

What to do When Your Furnace Refuses to Switch On

It might appear scary 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 avoid a furnace repair call with our DIY troubleshooting guide. You don’t need any technical skills. And most of these fixes are fast and affordable (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 Irvine, True Home Heating and Air Conditioning can lend a hand.

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 generally caused by forgotten routine maintenance. These checkups often highlight an expensive problem before it starts—and causes your HVAC system to fail.

During your appointment, 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

Take a Look at Your Thermostat

Start by examining your thermostat. Is it telling your furnace to switch on?

If you have a digital thermostat:

  • Replace the batteries if the screen is unresponsive. 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.”
  • Make sure the program is displaying the current day and time and is set to “run.” If you can’t alter 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 complications.
  • Set the temp to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should start within a few minutes. If it doesn’t, double check that it has power by moving the fan switch from “auto” to “on.” If the fan doesn’t start immediately, your furnace may not be connected to power.

If you’re utilizing a Wi-Fi thermostat—like one made by Nest, Ecobee, Lux, Honeywell or Bosch—refer to the manufacturer’s website for help. If you can’t get your smart thermostat to turn on, call us at 949-258-7259 for support.

Smart Thermostat

Check Breakers and Switches

If you’ve already checked your thermostat, you will have 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.
  • Locate 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 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 an expert from True Home Heating and Air Conditioning at 949-258-7259 as soon as possible.

Your furnace has at least one wall switch located on or near it—no matter how old it is or who made 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, blocked air filters often create issues that are easily avoidable.

  • Your furnace can overheat and shut down too soon, due to dust in the filter hampering airflow.
  • Your energy bills could increase, because your furnace is starting up more often.
  • Your furnace may have a shorter life span, because it has to work harder.
  • Your furnace could lose power, because an excessively dirty filter can cue 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 changing out your filter:

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

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 monthly. Pleated filters generally 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 replace your filter on a more regular basis.

Inspect Your Condensate Pan

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

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

  • If your pan has a PVC pipe/drain: Check 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: Take a look at the float switch. If the switch is “up” and there’s liquid in the pan, call us at 949-258-7259. You will likely need a more modern pump.

Look 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 somewhere on the outside of your furnace.

Reach out to us at 949-258-7259 if you see anything other than a stable, colored light or blinking green light. Your furnace is likely giving an error code that requires professional service.

Clean Your Flame Sensor

Is your furnace attempting to start but turning off without producing heat? A dirty flame sensor could be at fault. When this occurs, your furnace will try to start 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 turn 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 switched out for a new one. Or something else could be the issue. Call us at 949-258-7259 for help if this happens.

Relight the Pilot Light

If your furnace is an older design, its pilot light could be extinguished. 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.
  • Stop holding the “reset” button once the pilot light is lit.

Contact us at 949-258-7259 if you’ve followed the steps 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 work?

Call us today at 949-258-7259 or use our online scheduler. We’ll come out to your home and find out what’s wrong.

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