The furnace is the hero of a house in winter. But there’s one tiny part inside it that most homeowners don’t even know exists, let alone realize they’re supposed to clean – the flame sensor.
Left unchecked, this small but crucial component could shut off your furnace when you need it most, leaving you shivering and with a potentially eye-watering emergency call-out bill.
How To Clean a Furnace Flame Sensor
If your heating goes out, your furnace should be the first thing you check.
A flame sensor in a furnace is a thin metal rod that detects if the burner is lit after gas flows, preventing dangerous build-up if it cannot sense the flame. If the sensor becomes too dirty, it can shut off prematurely, turning off your furnace at the most critical time of the year. Luckily, it is a common heating problem that you can repair yourself with cleaning.
Before you can start with the cleaning tips, however, the first step is to turn off the power and the gas valve, advises Tamer Sayed, a licensed HVAC technician and the owner-operator of Tamas Mechanical.'
'Never attempt to clean the furnace (or any other electrical equipment for that matter) while the power is on,' he urges. It is one of the worst cleaning mistakes that risks your safety and your appliances. 'Aside from switching off the unit, turn off the circuit breaker for further safety.'
With the power shut off, you will need the following tools:
- A screwdriver with the appropriate head for your furnace. This Screwdriver set from Walmart comes with 59 heads, so you always have the right tool to hand.
- Fine steel wool, such as a Brillo pad from Amazon.
- A clean microfiber cloth, also from Walmart.
- Optional: Work gloves from Lowe's to protect your skin.
1. Locate and Remove the Sensor
Before setting your winter heating schedule, locate the sensor and remove it for cleaning.
To do this, Tamer explains, 'Remove the panel on your furnace and look inside the compartment. The flame sensor is typically located near the burner and resembles a small metal rod with a ceramic base. Once you've located the sensor, remove the screw that secures it in place. Then carefully pull it out.
'One tip when doing this: Take a picture of the location before removing the flame sensor,' he adds. 'Make sure you don't misplace the screw.' A magnetic parts tray from Walmart makes these types of delicate DIY tasks less risky, holding your parts in place.
2. Clean the Sensor
The flame sensor is one of the few things you should clean with steel wool around your home.
Tamer suggests, 'A steel wool works just fine for cleaning the flame sensor. I highly recommend a Brillo pad from Amazon.'
However, Matt Gorbacz, owner of Clean Air Technologies, advises, 'Use a fine-grit emery cloth, something like 400 or 600 grit, or a Scotch-Brite pad [also from Amazon]. I suggest you don’t use sandpaper as it is too rough and can ruin the coating.
'Lightly rub the rod to remove the carbon buildup. You don’t have to rub it roughly, just clean the soot off so it’s shiny again. To finish, polish the sensor with a soft microfiber cloth, removing any debris so that it shines.'
3. Replace the Sensor and Power
With the sensor clean, replace it and the screw before reattaching the panel front and turning the electricity and gas back on.
If the sensor is not in the right position, the furnace will not light again. Try replacing the sensor again to get the correct placement.
What to Shop
Brillo pads offer the perfect abrasive cleaning power for shifting tough soot buildup without damaging the sensor.
This extra-large screwdriver set offers many different heads to help you complete almost any DIY task.
These magnetic part trays stops small screws and parts from rolling away, so you never loose an essential component during a DIY.
These thin work gloves protect your skin from the soot and grime, but do not impede movement for accurate DIY.
Microfiber cloths are machine washable, meaning you can reuse them for years with proper care. Simply wash after use on a warm water cycle and gentle detergent (skip the softener) to sanitize.
These small detail cleaning brushes are ideal for targeting awkward spots that cloths can't reach, such as the location where your flame sensor lives.
Meet the Experts
As the owner and lead project manager at Tamas Mechanical, Tamer oversees all aspects of HVAC design, installation, and service for residential and light commercial projects across the GTA.
Since 1996, Matt Gorbacz has been helping New Jersey families and businesses breathe cleaner, healthier air. As the owner of Clean Air Technologies, he brings over 28 years of hands-on experience in air duct cleaning, dryer vent services, UV lamp installation, air quality assessments, and HVAC system care.
In the worst-case scenario, there are some ways to heat a house when the furnace goes out, should the flame sensor not be at fault. If this is the case, it is time to call a pro, advises Matt. 'The furnace might have dirty burners or a gas issue,' he warns.
