furnace repair

What to do When Your Furnace Will Not Switch On

It might seem stressful to troubleshoot your furnace when your heat won’t work. 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 mechanical skills. And most of these fixes are fast and inexpensive (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 Clackamas, Central Air Inc can lend a hand.

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 service appointments often disclose a costly problem before it starts—and causes your HVAC system to stop working.

During your appointment, our NATE-certified professionals will thoroughly 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 bill.

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

Steps for Troubleshooting Your Furnace

Inspect Your Thermostat

Start by looking at 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.
  • Confirm that the switch is set to “heat” instead of “off” or “cool.”
  • Find out 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 with the up/down arrows and press the “hold” button. This will force the furnace to start if thermostat programming is causing an issue.
  • 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, see if it has power by sliding the fan switch from “auto” to “on.” If the fan doesn’t work right away, your furnace may not have power.

If you’re connected to 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 turn on, call us at 503-389-5307 for support.

Smart Thermostat

Check Breakers and Switches

Next, you will have 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 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 Central Air Inc at 503-389-5307 immediately.

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

Replace Your Air Filter

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

  • Your furnace can overheat and turn off 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 fail permantly faster, because it has to work harder.
  • Your furnace could lose power, because an excessively dirty filter can cause 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 position depends upon what model of furnace you have.

Replace furnace filter

When replacing your filter:

  • Shut 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 damage.

To make the process easier in the future, 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 usually 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 on a more regular basis.

Inspect Your Condensate Pan

Condensate pans, or drain pans, capture water your furnace removes 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 open. 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: Check out the float switch. If the switch is “up” and there’s fluid in the pan, call us at 503-389-5307. You will probably need a more modern pump.

Look Inside Your Furnace

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

Call us at 503-389-5307 if you see anything other than a steady, colored light or blinking green light. Your furnace is probably giving an error code that requires professional assistance.

Clean Your Flame Sensor

Is your furnace attempting to start but shutting down without producing heat? A soiled flame sensor could be to blame. When this occurs, 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 alright 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 turn off the power. Shut off the gas also if your gas valve is not electric.
  • Take off 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 as usual. If it doesn’t kick on, the sensor might need to be replaced. Or something else could be wrong. Call us at 503-389-5307 for guidance if this happens.

Relight the Pilot Light

If your furnace is an older design, 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 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 503-389-5307 if you’ve followed the guide 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 503-389-5307 or use our online scheduler. We’ll come out to your home and find out what’s wrong.

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