furnace repair

What to do When Your Furnace Will Not Start

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

You might be able to avoid a furnace repair call with our DIY troubleshooting guide. You don’t need any industry skills. And most of these fixes are brief 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 need a pro in Huntsville, All Weather Heating & Air Conditioning Inc can help.

We work on 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 checkups often highlight a costly problem before it gets worse—and causes your HVAC system to break down.

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

Check 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 blank. 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 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 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 start shortly. If it doesn’t, double check that it has power by moving the fan switch from “auto” to “on.” If the fan doesn’t start instantly, your furnace may not have access to 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 advice. If you can’t get your smart thermostat to function properly, call us at 256-801-4701 for help.

Smart Thermostat

Check Breakers and Switches

Next, 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 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 goes back to “off” after you do this, leave it alone. Contact a professional from All Weather Heating & Air Conditioning Inc at 256-801-4701 as soon as possible.

Your furnace has at least one wall switch situated on or near it—no matter its age or brand.

  • 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 located? Look in your basement, garage or utility closet. It could also be placed in a crawl space or attic.)

Replace Your Air Filter

Dirty, closed off 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 increase, 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 extra 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 model of furnace you have.

Replace furnace filter

When switching out your filter:

  • Turn off your furnace completely.
  • Pull out 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 easier next time, 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 generally last about three months. You can also get a washable filter that will work for 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, 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: 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: Check out the float switch. If the switch is “up” and there’s water in the pan, call us at 256-801-4701. You will most likely need an updated 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.

Reach out to us at 256-801-4701 if you see anything other than a stable, colored light or blinking green light. Your furnace is likely giving an error code that needs professional help.

Clean Your Flame Sensor

Is your furnace attempting to start but turning off without blowing heat? A dirty flame sensor could be be the reason. 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 try 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.
  • 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.
  • Remount 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 switched out for a new one. Or something else could be wrong. Call us at 256-801-4701 for assistance 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 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.
  • Stop holding the “reset” button once the pilot light is lit.

Contact us at 256-801-4701 if you’ve followed the steps 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 256-801-4701 or use our online scheduler. We’ll come out to your home and identify what’s wrong.

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