My Furnace Will Not Stay Lit: Cleaning a Flame Sensor

A Common Gas Furnace Problem & How to Fix for $1!

While there are a lot of parts working inside your heating system, one of the most common reasons for a furnace breaking down is because of one particular part – the flame sensor.

Just Right Heating & Cooling has repaired furnaces in the Waterford Township area since 1982. We have seen just about every kind of heating problem there is, even the issue of a furnace that is not staying lit. Often a problem may seem big, but it can be easily fixed.

Sometimes we respond to a call from a homeowner who tells us that, up until recently, their furnace was working fine. They could hear the burners come on, but pretty quickly, the furnace shuts off. The furnace will not stay lit. This can be very confusing for a homeowner, but it is often a problem we can easily solve. Not only that, but it may also be one you can solve yourself!

This common furnace problem is a dirty flame sensor.

Clean furnace flame sensor in hand

What is a Flame Sensor?

A furnace flame sensor is a stainless-steel rod with a ceramic or porcelain cover. You’ll find it behind the burners, most typically on the opposite side of the ignitor. Its job is to sense when there is a flame. When there is, the flame sensor signals for your furnace to keep sending gas to keep the heat going.

How does a flame sensor work?

Your furnace control board sends electricity to the flame sensor, which carries the flame to the burner face. The sensor lets the control board know that the current flows, telling the control board to continue allowing gas to flow.

If the sensor doesn’t tell the control board that the current is going where it should, the gas valve closes, and the heat stops coming through your vents.

cleaning a flame sensor near burners inside a furnace will not stay lit

DIY Steps for a Cleaning a Flame Sensor

It is natural for a furnace sensor to become dirty over time. But if it gets too dirty, it could stop doing its job. The control board will not sense the current is flowing if the sensor is covered in too much build-up.

Fortunately, it is a pretty easy task.


Rubbing $1 dollar bill may clean a dirty flame sensor

    1. Turn off the furnace power switch.
    2. Remove the sensor rod. It should be easy to remove with a screwdriver. Do not use a wrench, as that could cause the sensor’s cover to crack.
    • Using a Scotch-Brite™ pad, rub the sensor rod to clean it of all dirt and gunk. Do not use anything harsh like sandpaper. You can use a dollar bill to clean it. Just fold the bill over the rod and, while tightly gripping it, rub it back and forth until the rod becomes somewhat shiny.

Do not touch the flame sensor with your fingers. The oils on your hands can get on the sensor and make it more prone to get dirty later.

Furnace Shutdown

A dirty sensor causing the ignition to go out over and over again may cause the furnace to stop working. This is likely a temporary shutdown but will need to be dealt with to get it up and running again soon.

This shut down happens with furnaces that have a particular safety function. If a furnace control board senses 5 failed ignition attempts, it shuts down the furnace automatically and stays off for a few hours.

There is a work-around to waiting. If there is no safety risk (like a gas leak), a furnace can be reset to bypass this wait. Turn off the furnace’s power switch and wait 10 seconds before turning it back on.

When to Replace the Sensor

You should be able to clean a sensor no matter how dirty it is sufficiently. But they are inexpensive parts, and you can replace one instead of trying to clean it. There are different shapes of flame sensors, so be sure you are purchasing the proper kind.

Type of flame sensor
Type of furnace sensor rod

What if Having a Clean Flame Sensor Doesn’t Fix the Problem?

If the furnace won’t stay lit after you have a clean sensor, the burner face might be dirty.

To clean it, remove the front plate of the burners with a screwdriver. Be careful not to bump the ignitor as they are fragile and can be damaged from the oils on your hands.

Individual burners typically pop out easily. You’ll likely find the burner closest to the flame sensor is the dirtiest. Clean it with sandpaper, steel wool, or Scotch-Brite pad.

Potential Electronic Issues When a Furnace Will Not Stay Lit

Cleaning a flame sensor or burners will not get the furnace running again if the problem is electronic. A wire may be broken, keeping the electric current from getting to the sensor. A trained HVAC technician can detect whatever the problem is and fix it.

Contact Just Right Heating & Cooling to handle whatever furnace repair or service you need.

We can repair and service any heating system or unit with a team full of qualified heating repair technicians. We provide service to homeowners and businesses in and around Waterford Township.

Rely on our team of highly trained and experienced technicians to get the job done quickly, professionally, and safely. Call us at 248-673-0438.

Just Right Heating & Cooling HVAC team in Waterford Township, MI

Leave a Comment