A dirty furnace flame sensor is one of the most common reasons a furnace lights, then shuts off before your home warms up. To clean it, turn off the power and gas, remove the sensor, gently wipe off the carbon buildup, then reconnect and test it. If the problem continues, call a heating professional.
Most homeowners aren’t sure how to clean the flame sensor on their furnace, yet this small part keeps the whole heating system running. With Pro Comfort Control AC & Heating Installation offering heating services in Sudbury, MA, you’re covered either way. Read on for the steps our team uses to get your furnace running efficiently again.
Key Points
- The furnace flame sensor is a thin metal rod that confirms a flame is present so gas keeps flowing safely.
- A dirty flame sensor can’t detect the flame, so the furnace shuts off and restarts, wasting energy.
- Carbon residue from normal combustion builds up on every flame sensor over time.
- Cleaning takes four steps: turn off the furnace, remove the sensor, clean it gently, then reconnect and test.
- If cleaning doesn’t fix the problem, the sensor may need replacing or another part may be at fault.
Why Should You Clean Your Furnace Flame Sensor?
You should clean your furnace flame sensor because a dirty sensor can’t detect the flame, which makes the furnace shut down again and again. The flame sensor is a metal rod that sticks out toward the burner and detects the heat of the flame. If the sensor doesn’t detect heat, it triggers a safety system that shuts the gas valve to prevent a potential gas leak.
A dirty surface keeps the furnace flame sensor from reading the flame properly. The furnace then shuts off and on, wasting energy. No modern furnace can run without a working flame sensor, so keeping it clean protects your household’s safety.
Common signs of a dirty flame sensor include:
- Short burner runs: The burners light, then shut off shortly after, because the sensor can’t confirm the flame.
- Repeated ignition attempts: The furnace clicks and tries to relight several times, which often ends in a safety lockout.
- Cool air from the vents: The blower runs while the burners stay off, which usually points to a flame safety shutoff.
- Flashing error codes: Many furnaces flash a code on the control board when the flame isn’t detected.
What Causes Furnace Flame Sensor Buildup?
Carbon residue from normal combustion causes furnace flame sensor buildup. Gas burns along with molecules and debris floating in the air, and those burned particles settle on the sensor surface as carbon. The industry has made several HVAC improvements over the years, but none have eliminated combustion byproducts.
Manufacturers make flame sensors sensitive on purpose to prevent hidden gas leaks and unwanted flames, so buildup is unavoidable. A dirty air filter, a dusty furnace area, and skipped tune-ups can speed it up.
How to Clean a Furnace Flame Sensor in 4 Steps
DIY flame sensor cleaning is possible, but professionals do it safely and quickly. A furnace has complex and potentially hazardous components, so call an expert if you’re unsure. Here’s how a team like Pro Comfort Control tackles a dirty flame sensor:
#1: Fully Turn Off the Furnace
Your furnace connects to an electrical power source. Cut that connection by flipping the furnace off-switch or shutting off the furnace breaker.
In homes with non-electric gas valve controls, the team shuts the gas valve by hand. Check your system manual if you aren’t sure how your furnace connects to the gas line.
#2: Take Out the Flame Sensor
You’ll usually find the flame sensor on or near the burner assembly. Professionals remove it only after confirming no power or gas is flowing to the furnace.
Removal depends on the access panel. Some models use a slide-and-detach design, while others need a screwdriver. The sensor connects to the panel by a wire, which the team disconnects for proper cleaning.
#3: Clean the Furnace Flame Sensor Gently
Professionals sometimes use fine-grit sandpaper or steel wool to gently remove carbon buildup from the sensor rod. Rubbing too hard can scratch and damage the sensor, so for light buildup, wiping the rod with a clean paper towel is the safer choice.
Check the power wire to the control panel too. You shouldn’t see any corrosion or gunk.
#4: Reconnect and Test Your Sensor
After cleaning, the technician reconnects the sensor to the control panel and closes the access panel. Then you can restore the electrical, gas, and other connections to the furnace.
Turn the furnace on and confirm the sensor works. Startup may take a little longer than usual while the furnace resets. If it won’t turn on or the problem returns, the furnace flame sensor may need replacement during a furnace repair visit.
How Often Should a Furnace Flame Sensor Be Cleaned?
The easiest way to keep a furnace flame sensor clean is to include it in your annual heating maintenance visit. A technician cleans and inspects the sensor before the cold season, along with the burners, filter, and ignition system. Our Comfort Club membership includes annual furnace maintenance and priority scheduling.
Still Shutting Off? Call Pro Comfort Control for Furnace Care
That’s how to clean the flame sensor on your furnace. If a clean sensor doesn’t fix the problem, the cause could be a faulty gas connection, an electrical issue, or a failing blower motor. An older furnace with repeat problems may be ready for furnace installation of a new, efficient system.
Pro Comfort Control AC & Heating Installation has over 25 years of experience helping Sudbury homeowners stay warm, no matter what furnace issues come up. Call the office or schedule your appointment today to get your furnace flame sensor checked.