furnace repair

What to do When Your Furnace Refuses to Start

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

You may be able to avoid a furnace repair call with our DIY troubleshooting guide. You don’t need any industry skills. And most of these fixes are fast and low-cost (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 require a pro in Oxford, Franklin's Heating & Air Conditioning, Inc. can help.

We repair and maintain 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 service appointments often reveal a high-cost problem before it begins—and causes your HVAC system to fail.

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

Steps for Troubleshooting Your Furnace

Inspect Your Thermostat

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

If you have a digital thermostat:

  • Change 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.”
  • Look to see if the program is displaying the right day and time and is set to “run.” If you can’t change the program, set the temperature with 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 temperature to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should kick on shortly. If it doesn’t, make sure it has power by moving the fan switch from “auto” to “on.” If the fan doesn’t run instantly, your furnace may not have 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 help. If you can’t get your smart thermostat to function properly, call us at 662-350-0343 for support.

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 touching the panel or breakers.
  • Locate 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 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 Franklin's Heating & Air Conditioning, Inc. at 662-350-0343 as soon as possible.

Your furnace has at least one wall switch located 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 located in a crawl space or attic.)

Replace Your Air Filter

Dirty, closed off air filters often generate problems 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 an extra 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 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 hurting your machine.

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 last about 10 years.

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

Inspect Your Condensate Pan

Condensate pans, or drain pans, capture 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: 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: Find the float switch. If the switch is “up” and there’s fluid in the pan, call us at 662-350-0343. You will probably need a more modern 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 kind, this light could be located on the outside of your furnace.

Call us at 662-350-0343 if you see anything other than a steady, colored light or blinking green light. Your furnace could be giving an error code that needs professional help.

Clean Your Flame Sensor

Is your furnace trying to start but shutting off without blowing heat? A dirty flame sensor could be at fault. When this occurs, your furnace will try to switch 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 take on 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 switch off the power. Shut off the gas as well if your gas valve is not electric.
  • Open 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.
  • 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 normally. If it doesn’t kick on, the sensor might need to be switched out for a new one. Or something else could be the problem. Call us at 662-350-0343 for help if this happens.

Relight the Pilot Light

If your furnace is an older design, 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.
  • Move the knob to “pilot.”
  • Hold down the “reset” button as you deliver the flame of a long lighter to the pilot light opening.
  • Let go of the “reset” button once the pilot light is lit.

Contact us at 662-350-0343 if you’ve followed the guide 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 start?

Call us today at 662-350-0343 or use our online scheduler. We’ll come out to your home and find out what’s wrong.

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