Tip & How-To about Heating & Cooling

Cleaning of flame sensors

In my experience I have seen many people use sand paper to clean the flame sensors on furnaces. It is best to use a small stainless steel brush to remove any chemicals that have been burned on the sensor. If you are cleaning the sensor you will want to remove it from the appliance and then hold it firmly while brushing off debri. Be sure to not loosen the sensing rod from the ceramic collar or it may move and cause a whole nother set of problems. The reason why I use a brush, a brush doesn't leave a silica residue on sensor that will become glass when heated further impeding the sensors job of sensing current through the burning gas.

Hope this helps
Greg B.

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blower comes on ,no flame most of the time,but when flame comes on it only lasts for a few minutes then stops. light flashes 4 times,i have replaced primary limeter to no avail.?

Your sensor is dirty. The sensor is the little rod that sticks in to the flame. It is just a little bigger around than a pencil lead and has one wire connected to it. It will be mounted just a few inches from the ignitor glow coil.
Turn power off to furnace
Take the sensor off
DO NOT wash it.
Take emory cloth or very light sand paper and lightly brush the steel rod of the sensor
You can also use a fine wire brush.
Put it back together and fire the furnace up again, chances are you've fixed your problem

May 28, 2011 | Goodman Heating & Cooling

1 Answer

furnace starts flame come on 3sec then goes out it doe,s this 10 times then starts and runs but air feels cold coming out warm not hot like before

Sounds like you could have 1 of 2 problems:

1. The flame sensor is dirty. The flame sensor is a small rod just a little bigger around than a pencil lead. It is located in the burner section just a few inches left or right from your glow ignitor. The flame will surround this sensor, but it the sensor is dirty, it cannot sense the heat of the flame. Take the sensor out of the furnace. It generally has one screw holding it, and one wire connected to it. Use emory cloth or light sand paper, or even a small wire brush to clean the sensor. DON'T GET IT WET.

2. You may have air in the gas line. This happens especially if the gas has been turned off to the house. You can bleed the gas line by loosening the gas line connected to the furnace. (furnace turned off) Bleed it just for 10 seconds or so, tighten the gas line, check for leaks with soapy water, and try the furnace again. You may have to do this more than once.

May 21, 2011 | Heating & Cooling

1 Answer

furnace will start and sequence fine run for five minutes or so then the flame cuts out....miller type furnace put a new board in last year so now it cycles three times and goes into soft lockout.. pressure switch seems fine as does the limit and roller switch...why would the flame just cut out...

Clean the flame sensor.

If your furnace lights and the gas stays on for 8 to 10 seconds, then shuts right back off, then you need to clean your flame sensor with light sand paper or steel wool. You might need a new flame sensor, but most of the time they can be cleaned an will work well after cleaning.

Nov 19, 2010 | Heating & Cooling

1 Answer

flame sensor

The flame sensor is located in the burner box of this unit. You may have to remove a cover plate to get to it. It will either look like a small probe or small diameter copper pipe (real small).


It will either be close to the pilot or ignitor or aways away where the flame has to travel to it.


A small brush or sand paper can be used to clean it.


If your furnace has more than one burner, while you are inside, clean out the track that allows the flame to travel to each burner. A small can of compressed air works great along with a small wire bruch.

Oct 16, 2007 | Goodman GMS90703BXA Heater

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