furnace repair

What to do When Your Furnace Will Not Start

It might seem scary to troubleshoot your furnace when your heat won’t run. But it doesn’t have to be that way.

You may be able to skip a furnace repair call with our DIY troubleshooting guide. You don’t need any industry skills. And the majority of these fixes are brief and affordable (or even free).

This list 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 require a pro in Carlsbad, Banister's Heating & Air Conditioning Services can lend a hand.

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

Furnace breakdowns are usually caused by forgotten routine maintenance. These evaluations often disclose an expensive problem before it begins—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-managed furnace often lasts longer and operates more efficiently, saving you more on your heating charges.

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

Steps for Troubleshooting Your Furnace

Take a Look at Your Thermostat

Start by examining your thermostat. Is it telling your furnace to turn on?

If you have a digital thermostat:

  • Change the batteries if the screen is off. 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.”
  • Find out if the program is presenting the right day and time and is set to “run.” If you can’t alter the program, fix the temperature by using the up/down arrows and press the “hold” button. This will require the furnace to switch 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 start within a few minutes. If it doesn’t, see if it has power by pushing the fan switch from “auto” to “on.” If the fan doesn’t run immediately, 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 help. If you can’t get your smart thermostat to function properly, call us at 575-446-3948 for assistance.

Smart Thermostat

Check Breakers and Switches

After that, 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 working with the panel or breakers.
  • Find 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 middle or “off” position.
  • With one hand, firmly push 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 Banister's Heating & Air Conditioning Services at 575-446-3948 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? 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 complications 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 a very 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 location depends upon what kind of furnace you have.

Replace furnace filter

When switching out your filter:

  • Shut off your furnace completely.
  • Grab 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 less difficult in the future, 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 generally last about three months. You can also get a washable filter that will be good for about 10 years.

If you have children or pets, you may need to replace your filter more often.

Look at Your Condensate Pan

Condensate pans, or drain pans, catch water your furnace pulls 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 575-446-3948. You will likely need a new pump.

Check Inside Your Furnace

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

Reach out to us at 575-446-3948 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 help.

Clean Your Flame Sensor

Is your furnace making an effort to start but turning off without producing heat? A soiled flame sensor could be to blame. When this takes place, 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 switch off the power. Shut off the gas as well if your gas valve is not electric.
  • Remove your furnace’s front panel and track 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 updated. Or something else could be the problem. Call us at 575-446-3948 for guidance if this happens.

Relight the Pilot Light

If your furnace is an older model, its pilot light could be blown out. 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.
  • 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.

Call us at 575-446-3948 if you’ve followed the steps 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 turn on?

Call us today at 575-446-3948 or use our online scheduler. We’ll come out to your home and figure out what’s wrong.

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