furnace repair

What to do When Your Furnace Refuses to Start

It might appear stressful to troubleshoot your furnace when your heat won’t work. 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 industry skills. And the majority of these fixes are quick and affordable (or even free).

This guide 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 Huffman, Air Houston Mechanical LLC can help.

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 usually caused by neglected routine maintenance. These checkups often highlight a high-cost 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-maintained furnace often lasts longer and operates more efficiently, saving you more on your heating charges.

Ready to begin troubleshooting your furnace? Follow our step-by-step guide below.

Steps for Troubleshooting Your Furnace

Check 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 blank. If the digital screen is scrambled, you may need a different thermostat.
  • See if that the switch is set to “heat” instead of “off” or “cool.”
  • Look to see if the program is presenting the current day and time and is set to “run.” If you can’t alter the program, change the temperature with the up/down arrows and press the “hold” button. This will compel the furnace to start if thermostat programming is causing an issue.
  • Set the thermostat 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 work right away, 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—check the manufacturer’s website for help. If you can’t get your smart thermostat to turn on, call us at 832-777-1521 for support.

Smart Thermostat

Check Breakers and Switches

After that, 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.
  • 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 shift 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 Air Houston Mechanical LLC at 832-777-1521 as soon as possible.

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

Replace Your Air Filter

Dirty, blocked air filters often cause complications that are easily avoidable.

  • Your furnace can overheat and shut down too soon, due to dust in the filter restricting airflow.
  • Your energy bills could climb, 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 find 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 replacing your filter:

  • Turn off your furnace completely.
  • Pull out 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 damage.

To make the process simpler next time, use a permanent marker on your furnace housing or ductwork to indicate the airflow direction and filter size.

We suggest replacing flat filters monthly. 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 replace your filter on a more regular basis.

Inspect Your Condensate Pan

Condensate pans, or drain pans, catch water your furnace takes 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 clear. 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 832-777-1521. You will likely need a more modern pump.

Check Inside Your Furnace

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

Reach out to us at 832-777-1521 if you see anything other than a stable, colored light or blinking green light. Your furnace could be giving an error code that demands professional assistance.

Clean Your Flame Sensor

Is your furnace attempting to start but shutting off without generating heat? A filthy flame sensor could be to blame. When this occurs, your furnace will try to turn 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 confident opening up your furnace. We can also do it for you.

Want 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 switch off the power. Shut off the gas as well if your gas valve is not electric.
  • Take off your furnace’s front panel and trace 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 regularly. If it doesn’t turn on, the sensor might need to be updated. Or something else could be wrong. Call us at 832-777-1521 for help if this happens.

Relight the Pilot Light

If your furnace is an older style, its pilot light could be out. 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 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 832-777-1521 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 start?

Call us today at 832-777-1521 or use our online scheduler. We’ll come out to your home and find out what’s wrong.

*Required fields