furnace repair

What to do When Your Furnace Will Not Switch On

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

You might be able to skip a furnace repair call with our DIY troubleshooting guide. You don’t need any technical skills. And many of these fixes are quick and affordable (or even free).

This guide will walk you through how to fix your furnace when it won’t start, won’t stay on or won’t light.

When you require a pro in Marshalltown, B & G HVAC can be there.

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 a lack of routine maintenance. These evaluations often disclose a high-cost problem before it gets worse—and causes your HVAC system to fail.

During our visit, 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 bill.

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

Steps for Troubleshooting Your Furnace

Inspect Your Thermostat

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

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.
  • Check that that the switch is set to “heat” instead of “off” or “cool.”
  • Make sure the program is presenting the right day and time and is set to “run.” If you can’t override the program, change the temperature by using 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 thermostat to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should turn on shortly. 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 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 help. If you can’t get your smart thermostat to work, call us at 641-812-2044 for assistance.

Smart Thermostat

Check Breakers and Switches

After that, you will want to make sure your breakers and furnace switch are on.

  • Find 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 handling 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 B & G HVAC at 641-812-2044 immediately.

Your furnace has at least one wall switch located 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 to find your furnace? 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 create complications that are easily avoidable.

  • Your furnace can overheat and stop working too soon, due to dust in the filter restricting airflow.
  • Your energy bills could get more expensive, because your furnace is starting up 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 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 replacing 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.
  • Replace the new filter with the arrow pointing toward the furnace to avoid hurting your machine.

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

We recommend replacing flat filters each month. Pleated filters typically 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 replace your filter more frequently.

Inspect Your Condensate Pan

Condensate pans, or drain pans, hold 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: Be 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 liquid in the pan, call us at 641-812-2044. You will probably need an updated pump.

Check Inside Your Furnace

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

Call us at 641-812-2044 if you see anything other than a steady, colored light or blinking green light. Your furnace is probably giving an error code that demands professional help.

Clean Your Flame Sensor

Is your furnace attempting to start but shutting off without producing heat? A dirty flame sensor could be be the reason. 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 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 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.
  • 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 replaced. Or something else could be the issue. Call us at 641-812-2044 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 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 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 641-812-2044 if you’ve followed the steps 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 work?

Call us today at 641-812-2044 or use our online scheduler. We’ll come out to your home and figure out what’s wrong.

*Required fields