furnace repair

What to do When Your Furnace Will Not Turn On

It might feel overwhelming to troubleshoot your furnace when your heat won’t turn on. But it doesn’t have to be that way.

You could be able to skip a furnace repair call with our DIY troubleshooting guide. You don’t need any industry skills. And most of these fixes are fast and inexpensive (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 need a pro in Derby, Giordanos Heating and Air Conditioning can help.

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 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 operating properly and lubricate moving parts. A well-kept furnace often lasts longer and operates more efficiently, saving you more on your heating costs.

Ready to begin 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 switch on?

If you have a digital thermostat:

  • Change the batteries if the screen is off. 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.”
  • Find out 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 by using the up/down arrows and press the “hold” button. This will force the furnace to switch on if thermostat programming is causing a problem.
  • Set the thermostat to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should kick on fairly quickly. If it doesn’t, double check that it has power by sliding the fan switch from “auto” to “on.” If the fan doesn’t start right away, your furnace may not have 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 function properly, call us at 203-734-7648 for help.

Smart Thermostat

Check Breakers and Switches

Next, you will need 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 working with the panel or breakers.
  • Find the breaker labeled “furnace” or “heat” and confirm that it’s switched in the “on” position. If the breaker has tripped, it will be in the center 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 a technician from Giordanos Heating and Air Conditioning at 203-734-7648 right away.

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 get working 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, clogged air filters often create problems 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 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 location depends upon what type of furnace you have.

Replace furnace filter

When replacing your filter:

  • Turn off your furnace completely.
  • Grab 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.
  • Put in the new filter with the arrow pointing toward the furnace to avoid damage.

To make the process simpler 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 each 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 change your filter more often.

Inspect Your Condensate Pan

Condensate pans, or drain pans, hold 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: Check 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: Find the float switch. If the switch is “up” and there’s liquid in the pan, call us at 203-734-7648. You will probably need a more modern pump.

Peek Inside Your Furnace

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

Call us at 203-734-7648 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 service.

Clean Your Flame Sensor

Is your furnace attempting to start but shutting off without generating heat? A soiled flame sensor could be at fault. When this occurs, 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 alright 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 shut off the power. Shut off the gas also if your gas valve is not electric.
  • Open 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 start, the sensor might need to be replaced. Or something else could be the problem. Call us at 203-734-7648 for help if this happens.

Relight the Pilot Light

If your furnace is an older model, its pilot light could be extinguished. Relight it following the instructions on the label. You can locate 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.
  • Release the “reset” button once the pilot light is lit.

Reach out to us at 203-734-7648 if you’ve followed the instructions 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 start?

Call us today at 203-734-7648 or use our online scheduler. We’ll come out to your home and identify what’s wrong.

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