furnace repair

What to do When Your Furnace Will Not 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 could be able to avoid a furnace repair call with our DIY troubleshooting guide. You don’t need any mechanical skills. And many of these fixes are quick and affordable (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 Rochester, Brogan Heating & AC Inc can help.

We repair and maintain 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 checkups often reveal a costly problem before it starts—and causes your HVAC system to fail.

During your appointment, our NATE-certified professionals will closely inspect your furnace, make sure it’s working properly and lubricate moving parts. A well-kept 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

Inspect Your Thermostat

Start by checking your thermostat. Is it telling your furnace to start?

If you have a digital thermostat:

  • Switch out 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.”
  • Look to see if the program is displaying the correct day and time and is set to “run.” If you can’t override the program, set the temperature by pushing the up/down arrows and press the “hold” button. This will require the furnace to turn 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, make sure it has power by pushing 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 utilizing 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 507-218-0088 for assistance.

Smart Thermostat

Check Breakers and Switches

If you’ve already checked your thermostat, you will want to make sure your breakers and furnace switch are on.

  • Go 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.
  • 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 goes back to “off” after you do this, leave it alone. Contact a technician from Brogan Heating & AC Inc at 507-218-0088 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 get working 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 generate issues 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 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 an excessively 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 placement depends upon what model of furnace you have.

Replace furnace filter

When changing out your filter:

  • Shut down 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 hurting your machine.

To make the process easier for yourself, use a permanent marker on your furnace housing or ductwork to indicate the airflow direction and filter size.

We suggest 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 change 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 seeping water or there’s standing water in the pan.

  • If your pan has a PVC pipe/drain: Make 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 507-218-0088. You will likely need a more modern pump.

Look Inside Your Furnace

You can check the status 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 507-218-0088 if you see anything other than a steady, colored light or blinking green light. Your furnace is likely giving an error code that needs professional assistance.

Clean Your Flame Sensor

Is your furnace making an effort to start but shutting down without generating heat? A soiled flame sensor could be to blame. When this takes place, 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 comfortable 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 shut 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.
  • 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 turn on, the sensor might need to be switched out for a new one. Or something else could be the problem. Call us at 507-218-0088 for assistance 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 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.
  • Turn the knob to “pilot.”
  • Hold down the “reset” button as you move the flame of a long lighter to the pilot light opening.
  • Release the “reset” button once the pilot light is lit.

Contact us at 507-218-0088 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 turn on?

Call us today at 507-218-0088 or use our online scheduler. We’ll come out to your home and identify what’s wrong.

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