furnace repair

What to do When Your Furnace Will Not Turn On

It might seem stressful to troubleshoot your furnace when your heat won’t run. 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 technical skills. And most 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 turn on, won’t stay on or won’t light.

When you require a pro in Robstown, McNatt Inc can be there.

We work on 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 neglected routine maintenance. These evaluations often disclose a costly problem before it gets worse—and causes your HVAC system to stop working.

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

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 start?

If you have a digital thermostat:

  • Replace the batteries if the screen is blank. If the digital screen is scrambled, you may need to replace your thermostat.
  • Check that that the switch is set to “heat” instead of “off” or “cool.”
  • Make sure the program is displaying the current day and time and is set to “run.” If you can’t alter 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 temp to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should turn on fairly quickly. If it doesn’t, make sure it has power by sliding the fan switch from “auto” to “on.” If the fan doesn’t run immediately, your furnace may not have access to power.

If you’re using a Wi-Fi thermostat—like one made by Nest, Ecobee, Lux, Honeywell or Bosch—refer to the manufacturer’s website for guidelines. If you can’t get your smart thermostat to function properly, call us at 361-247-0605 for help.

Smart Thermostat

Check Breakers and Switches

After that, you will need 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.
  • Pinpoint 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 midpoint 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 McNatt Inc at 361-247-0605 immediately.

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 kick on if the switch was off. (Not sure where your furnace is located? Look in your basement, garage or utility closet. It could also be placed in a crawl space or attic.)

Replace Your Air Filter

Dirty, clogged air filters often generate problems that are easily avoidable.

  • Your furnace can overheat and shut down too soon, due to dust in the filter diminishing 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 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 position depends upon what model 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.
  • Put in the new filter with the arrow pointing toward the furnace to avoid damaging your system.

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 advise replacing flat filters once a month. Pleated filters usually last about three months. You can also get a washable filter that will work for about 10 years.

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

Look at Your Condensate Pan

Condensate pans, or drain pans, capture water your furnace pulls 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: Be 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 water in the pan, call us at 361-247-0605. You will likely need a more modern pump.

Look Inside Your Furnace

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

Contact us at 361-247-0605 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 service.

Clean Your Flame Sensor

Is your furnace attempting to start but turning off without producing heat? A filthy flame sensor could be be the reason. When this happens, 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.

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 shut off the power. Shut off the gas also 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.
  • Replace 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 start, the sensor might need to be switched out for a new one. Or something else could be the issue. Call us at 361-247-0605 for assistance if this happens.

Relight the Pilot Light

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

Call us at 361-247-0605 if you’ve followed the instructions 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 361-247-0605 or use our online scheduler. We’ll come out to your home and find out what’s wrong.

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