furnace repair

What to do When Your Furnace Will Not Turn On

It might feel scary to troubleshoot your furnace when your heat won’t work. 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 many of these fixes are quick 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 have to have a pro in Rock Hill, US Air Heating and Cooling can help.

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

Furnace breakdowns are usually caused by neglected routine maintenance. These service appointments often reveal a costly problem before it starts—and causes your HVAC system to stop working.

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

Ready to start 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 switch on?

If you have a digital thermostat:

  • Change the batteries if the screen is blank. If the digital screen is scrambled, you may need a new thermostat.
  • Check that that the switch is set to “heat” instead of “off” or “cool.”
  • Find out if the program is displaying the right day and time and is set to “run.” If you can’t change the program, change the temperature with the up/down arrows and press the “hold” button. This will require the furnace to switch on if thermostat programming is causing a problem.
  • Set the temp to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should turn on within a few minutes. If it doesn’t, double check that it has power by pushing the fan switch from “auto” to “on.” If the fan doesn’t start instantly, 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 advice. If you can’t get your smart thermostat to turn on, call us at 803-220-0761 for help.

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.

  • 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 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 middle or “off” position.
  • With one hand, firmly move 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 US Air Heating and Cooling at 803-220-0761 right away.

Your furnace has at least one wall switch placed 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 start if the switch was off. (Not sure where your furnace is located? 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 create problems that are easily avoidable.

  • Your furnace can overheat and stop working too soon, due to dust in the filter hampering airflow.
  • Your energy bills could get more expensive, because your furnace is turning on more often.
  • Your furnace may not last as long, because it has to work harder.
  • Your furnace could lose power, because a very dirty filter can prompt the breaker to trip.

You can locate 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 switching out your filter:

  • Shut off your furnace completely.
  • Pick up the filter, hold it up to the light and look through it. Place a new filter in your system 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 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 once a month. Pleated filters typically 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 change your filter more often.

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 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 803-220-0761. You will most likely need a new pump.

Look 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.

Call us at 803-220-0761 if you see anything other than a stable, colored light or blinking green light. Your furnace is probably giving an error code that needs professional assistance.

Clean Your Flame Sensor

Is your furnace attempting to start but turning off without generating heat? A soiled flame sensor could be to blame. When this happens, 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.

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 regularly. If it doesn’t kick on, the sensor might need to be updated. Or something else could be the issue. Call us at 803-220-0761 for assistance if this happens.

Relight the Pilot Light

If your furnace is an older model, its pilot light could be 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.
  • Turn the knob to “pilot.”
  • Hold down the “reset” button as you bring the flame of a long lighter to the pilot light opening.
  • Release the “reset” button once the pilot light is lit.

Contact us at 803-220-0761 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 803-220-0761 or use our online scheduler. We’ll come out to your home and figure out what’s wrong.

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