furnace repair

What to do When Your Furnace Wont Switch On

It might seem 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 industry skills. And many of these fixes are quick and inexpensive (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 have to have a pro in Tucker, ACS Heating and Air Conditioning 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 evaluations often reveal a high-cost problem before it gets worse—and causes your HVAC system to fail.

During our visit, our NATE-certified professionals will thoroughly inspect your furnace, make sure it’s working 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 start troubleshooting your furnace? Follow our step-by-step guide below.

Steps for Troubleshooting Your Furnace

Take a Look at Your Thermostat

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

If you have a digital thermostat:

  • Switch out the batteries if the screen is unresponsive. If the digital screen is scrambled, you may need a new thermostat.
  • See if that the switch is set to “heat” instead of “off” or “cool.”
  • Look to see if the program is displaying the right day and time and is set to “run.” If you can’t override the program, change the temperature by using the up/down arrows and press the “hold” button. This will force the furnace to start if thermostat programming is causing complications.
  • Set the temperature to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should start shortly. If it doesn’t, make sure it has power by moving the fan switch from “auto” to “on.” If the fan doesn’t start instantly, your furnace may not have 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 function properly, call us at 770-450-1539 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.

  • 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.
  • 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 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 a professional from ACS Heating and Air Conditioning at 770-450-1539 as soon as possible.

Your furnace has at least one wall switch situated 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 get working if the switch was off. (Not sure where your furnace is located? 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 create complications 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 get more expensive, because your furnace is working more often.
  • Your furnace may have a shorter life span, because it has to work harder.
  • Your furnace could lose power, because an extra dirty filter can prompt 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 location depends upon what model of furnace you have.

Replace furnace filter

When replacing your filter:

  • Shut down 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.
  • Put in the new filter with the arrow pointing toward the furnace to avoid damage.

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

We advise replacing flat filters monthly. Pleated filters usually 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 on a more regular basis.

Check Out Your Condensate Pan

Condensate pans, or drain pans, catch water your furnace removes 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: Make 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: Take a look at the float switch. If the switch is “up” and there’s fluid in the pan, call us at 770-450-1539. You will most likely need a new pump.

Check Inside Your Furnace

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

Reach out to us at 770-450-1539 if you see anything other than a steady, colored light or blinking green light. Your furnace could be giving an error code that demands professional service.

Clean Your Flame Sensor

Is your furnace making an effort to start but shutting off without producing heat? A soiled flame sensor could be at fault. When this happens, 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 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 turn off the power. Shut off the gas too if your gas valve is not electric.
  • Take off your furnace’s front panel and follow 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.
  • Remount 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 start, the sensor might need to be replaced. Or something else could be the problem. Call us at 770-450-1539 for guidance if this happens.

Relight the Pilot Light

If your furnace is an older model, its pilot light could be extinguished. 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.
  • Switch 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.

Call us at 770-450-1539 if you’ve followed the instructions 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 work?

Call us today at 770-450-1539 or use our online scheduler. We’ll come out to your home and find out what’s wrong.

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