When your furnace won’t start, doing your own furnace repair in Florissant and St. Charles, Missouri, can feel pretty overwhelming.

Figuring out a furnace-related problem might feel like a daunting process when your heat won’t start. But it doesn’t have to be like that.

There are a few speedy, low-cost fixes you can do on your own to prevent a furnace repair call.

If your furnace won’t turn on, won’t stay on or won’t ignite, try the troubleshooting list below before getting in touch with an HVAC professional.

If you find you need help from a heating and cooling expert and live in Florissant and St. Charles, B & B Heating & Cooling can assist you. We can repair most types of heating systems and also provide emergency furnace repair.

If you’re ready for a new heating system, we also do furnace installation.

While you’re talking with us, think about an annual furnace maintenance plan that might help you avoid problems in the future. We can tell you how often your furnace should be inspected by one of our NATE-Certified professionals.

Use our easy guide below to start troubleshooting your furnace. Most of these steps don’t require mechanical abilities.

Furnace Repair Checklist

1. Check the Thermostat

To start, make sure your thermostat is signaling your furnace to ignite.

Digital Thermostat

Replace the batteries if the screen is blank. If the digital screen is jumbled, the thermostat may need to be replaced.

Make sure the switch is set to “heat” rather than “off” or “cool.”

Ensure the program is displaying the correct day and time and is set to “run.” If you’re having trouble overriding the program, set the temperature by using the up/down arrows and press the “hold” button. This will force the furnace to ignite if thermostat programming is causing trouble.

Increase the temperature setting to 5 degrees warmer than the room temperature.

If your furnace hasn’t kicked on within few minutes, make sure it has power by toggling the fan switch from “auto” to “on.” If the fan doesn’t run, your furnace may not have power.

Smart Thermostat

If you have a smart thermostat—like one made by Nest, Ecobee, Lux, Honeywell or Bosch—troubleshooting is very model-specific. Take a look at the manufacturer’s website for help. If you still can’t get your Wi-Fi thermostat to work, call us at 314-325-7552 for heating and cooling service.

2. Examine Breakers and Switches

Next, you will need to check if your breaker and furnace switch are on.

Look for your house’s main electrical panel. If you aren’t sure where it is, look for a gray metal box in your basement, garage or closet.

Make sure your hands and feet are dry before touching the panel or breakers.

Look for the breaker labeled “furnace” or “heat,” and make sure it’s switched “on.” If the breaker has tripped, it will be in the middle or “off” position.

Using one hand, firmly switch the breaker to the “on” position. If the breaker immediately trips and pops back to “off,” don’t try to reset it and call a professional from B & B Heating & Cooling at 314-325-7552 right away.

No matter your furnace’s age or brand, it has at least one standard wall switch located on or by it.

Make sure the switch is flipped up in the “on” position. If it was turned off, anticipate your furnace could take up to five minutes to turn on. (If you don’t know where to find your furnace, take a look at your basement, garage or utility closet. It could also be in a crawl space or attic.)

3. Replace the Air Filter

When it comes to furnace breakdown, a grungy, clogged air filter is regularly the top offender.

If your filter is too dirty:

  • Your furnace won’t keep heating your home, or it could overheat from limited airflow.
  • Your energy bills could be higher because your furnace is turning on more often.
  • Your furnace could fail too soon because a dirty filter causes it to work overtime.
  • Your furnace can be cut off from power if an overly dirty filter causes the breaker to trip.

Depending on what type of furnace you own, your air filter is located inside the blower compartment of your furnace, an attached filter case or wall-mounted return air grille.

To replace your filter:

  1. Turn off your furnace.
  2. Pull out the filter and angle it toward the light. If you can’t see light through it, use a new one.
  3. Insert the new filter with the arrow pointing toward the furnace to avoid damage.

Flat filters should be replaced once a month, while pleated filters should last about three months. You can also buy a washable filter that will last about 10 years. If you have children or pets, you may have to put in a new filter more frequently.

To make the process smoother in the future, use a permanent marker on your furnace housing or ductwork to list the airflow direction and filter size.

4. Inspect the Condensate Pan

Commonly known as drain pans, condensate pans hold water your furnace draws from the air.

If water is dripping out of your furnace or its pan has standing water in it, follow these steps.

  • If your pan has a drain (look for a PVC pipe), check that it isn’t full. If it needs to be drained, use a special pan-cleaning tablet you can buy at home improvement or hardware stores.
  • If your pan has a pump, take a look at the float switch. If the switch is stuck “up” with water in the pan, contact us at 314-325-7552, because you will probably need a new pump.

5. Check for Furnace Error Codes

If malfunctions keep on happening, peek inside your furnace’s plastic window to verify the status of the blower motor. Depending on the model, the light could also be attached on the outside of your furnace.

If you see anything else besides a steady, colored light or blinking green light, call us at 314-325-7552 for HVAC service. Your furnace may be giving an error code that requires professional service.

6. Clean the Flame Sensor

If your furnace tries to start but shuts off without distributing heat, a dirty flame sensor could be to blame. When this takes place, your furnace will make an attempt to turn on three times before a safety feature shuts it down for about an hour.

If you feel comfortable with opening up your furnace, cleaning your flame sensor is something you can do yourself. Or, one of our heating service specialists can do it for you.

If you want to clean the sensor yourself, you’ll need:

  • A 1/4” hex screwdriver or wrench
  • Piece of light grit sandpaper, steel wool or emery cloth
  • A dry, clean paper towel

Next:

  • Shut off the furnace’s power by using its wall switch or breaker. If your gas valve is not electric, you will need to shut off the gas as well.
  • Take off the furnace’s front panel and track the wire to the flame sensor.
  • Unscrew the rod and use your sandpaper, steel wool or emery cloth to gently rub the metal rod.
  • Wipe off the rod with a paper towel.
  • Remount the sensor.
  • Replace the furnace doors.
  • Turn the furnace’s power back on. It could run through a set of checks before proceeding with normal operation. If your furnace doesn’t start, the sensor may need to be replaced or something else may be wrong. If this happens, get in touch with us at 314-325-7552 for heating and cooling repair assistance.

7. Relight the Pilot Light

If you are using an older furnace, the pilot light could be out. To relight it, find the instructions on a label on your furnace, or follow these steps.

  • Locate the switch on the bottom of your furnace labeled “pilot,” “on” and “off.”
  • Turn the switch to the “off” position.
  • Wait at least five minutes to avoid possibly creating a fire.
  • Turn the knob to “pilot.”
  • Push 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.

If you have followed the instructions twice and the pilot light still won’t light or stay lit, contact us at 314-325-7552 for furnace service.

Check Your Fuel Source

Try turning on another gas appliance. If it doesn’t work, your natural gas service could be turned off, or you could be out of propane.

We Can Help with HVAC Repair

Followed our troubleshooting guide but your furnace still won’t work?

Call us today at 314-325-7552 or contact us online. We’ll come out and figure out the problem.

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