furnace repair

What to do When Your Furnace Wont Start

It might feel scary to troubleshoot your furnace when your heat won’t run. 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 most 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 turn on, won’t stay on or won’t light.

When you need a pro in Liberty, Air Unlimited Heating & Cooling can help.

We work on 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 generally caused by forgotten routine maintenance. These checkups often disclose a costly problem before it begins—and causes your HVAC system to stop working.

During your appointment, our NATE-certified professionals will carefully inspect your furnace, make sure it’s operating properly and lubricate moving parts. A well-managed furnace often lasts longer and operates more efficiently, saving you more on your heating costs.

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 switch on?

If you have a digital thermostat:

  • Switch out the batteries if the screen is blank. 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 correct day and time and is set to “run.” If you can’t change the program, change the temperature by using the up/down arrows and press the “hold” button. This will force the furnace to switch on if thermostat programming is causing complications.
  • Set the thermostat to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should turn 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 work instantly, your furnace may not be connected to power.

If you’re connected to a Wi-Fi thermostat—like one made by Nest, Ecobee, Lux, Honeywell or Bosch—turn to the manufacturer’s website for guidelines. If you can’t get your smart thermostat to work, call us at 816-286-7258 for assistance.

Smart Thermostat

Check Breakers and Switches

After that, you will want to make sure your breakers and furnace switch are on.

  • Find 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 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 shift the breaker to the “on” position. If the breaker trips and moves back to “off” after you do this, leave it alone. Contact a professional from Air Unlimited Heating & Cooling at 816-286-7258 right away.

Your furnace has at least one wall switch situated 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, clogged air filters often cause 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 climb, 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 excessively 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 type 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. Get a new filter 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 for yourself, use a permanent marker on your furnace housing or ductwork to indicate the airflow direction and filter size.

We recommend replacing flat filters once a 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 replace your filter on a more regular basis.

Look at Your Condensate Pan

Condensate pans, or drain pans, hold water your furnace takes from the air.

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

  • If your pan has a PVC pipe/drain: Be 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: Find the float switch. If the switch is “up” and there’s fluid in the pan, call us at 816-286-7258. You will most likely need a more modern pump.

Peek Inside Your Furnace

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

Call us at 816-286-7258 if you see anything other than a solid, colored light or blinking green light. Your furnace is probably giving an error code that needs professional help.

Clean Your Flame Sensor

Is your furnace trying to start but shutting off without generating heat? A dirty flame sensor could be be the reason. 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 confident opening up your furnace. We can also do it for you.

Ready 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 shut off the power. Shut off the gas too if your gas valve is not electric.
  • Remove 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 as usual. If it doesn’t start, the sensor might need to be switched out for a new one. Or something else could be the issue. Call us at 816-286-7258 for guidance if this happens.

Relight the Pilot Light

If your furnace is an older style, its pilot light could be extinguished. Relight it following the instructions on the label. You can read 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.
  • Release the “reset” button once the pilot light is lit.

Contact us at 816-286-7258 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 816-286-7258 or use our online scheduler. We’ll come out to your home and figure out what’s wrong.

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