furnace repair

What to do When Your Furnace Wont Start

It might seem scary 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 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 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 need a pro in Drexel Hill, O'Brien Heating & Air Conditioning can help.

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 generally caused by forgotten routine maintenance. These evaluations often highlight a costly problem before it gets worse—and causes your HVAC system to break down.

During our visit, our NATE-certified professionals will carefully 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 examining your thermostat. Is it telling your furnace to turn 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 new thermostat.
  • Check that that the switch is set to “heat” instead of “off” or “cool.”
  • Make sure the program is displaying the current day and time and is set to “run.” If you can’t change the program, fix the temperature by using the up/down arrows and press the “hold” button. This will compel the furnace to start if thermostat programming is causing a problem.
  • Set the temperature to 5 degrees warmer than the room’s temperature.
Digital Thermostat

Your furnace should start within a few minutes. If it doesn’t, see if it has power by sliding the fan switch from “auto” to “on.” If the fan doesn’t run 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—turn to the manufacturer’s website for help. If you can’t get your smart thermostat to turn on, call us at 610-257-7035 for assistance.

Smart Thermostat

Check Breakers and Switches

If you’ve already checked your thermostat, you will need 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 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 technician from O'Brien Heating & Air Conditioning at 610-257-7035 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 in a crawl space or attic.)

Replace Your Air Filter

Dirty, clogged air filters often create issues 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 increase, 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 cue 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 position depends upon what kind 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. 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 hurting your machine.

To make the process simpler in the future, 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 generally 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 switch out your filter on a more regular basis.

Check Out Your Condensate Pan

Condensate pans, or drain pans, capture water your furnace removes from the air.

Follow these steps if your furnace is dripping 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: Check out the float switch. If the switch is “up” and there’s liquid in the pan, call us at 610-257-7035. You will most likely need an updated pump.

Check Inside Your Furnace

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

Reach out to us at 610-257-7035 if you see anything other than a solid, colored light or blinking green light. Your furnace could be giving an error code that requires professional service.

Clean Your Flame Sensor

Is your furnace trying to start but turning off without blowing heat? A dirty flame sensor could be at fault. When this happens, 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.

Hoping 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 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.
  • 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 replaced. Or something else could be the issue. Call us at 610-257-7035 for guidance if this happens.

Relight the Pilot Light

If your furnace is an older style, its pilot light could be blown 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.
  • Stop holding the “reset” button once the pilot light is lit.

Reach out to us at 610-257-7035 if you’ve followed the instructions 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 turn on?

Call us today at 610-257-7035 or use our online scheduler. We’ll come out to your home and find out what’s wrong.

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