Is your furnace having trouble staying on once it fires up? Does it quickly shut off, after you start it? Does it do this a few times and then fully shuts down? Many homeowners have this problem every year because of a dirty flame sensor.
Heating, Ventilation, and Air Conditioning is a complex industry, but this repair is simple enough that you can perform by yourself.
In our example will show a gas-fired furnace, but you can find flame sensors in boilers and other gas-burning appliances.
To avoid danger, it is very important to shut off the power to your furnace (or any other appliance), prior to making any repairs. There will usually be a light switch (toggle switch) on or near your furnace. If this switch is not present, furnaces have a dedicated breaker; locate your furnace breaker and shut your unit down. NOTE: Turning off the thermostat does not shut down the power to your unit. Also, there are many different types of furnaces and appliances; if your gas valve is not electrically controlled, you will need to shut off the gas to the unit as well. Should you be confused about any of the information provided here, because it does not match with what you see on your unit, STOP! Do not guess or assume anything when dealing with your heating system. Call an HVAC professional in your area, in order to complete the repair on your unit.
Remove the Sensor. In the video, you can see 4 burner ports. Between the 1st and 2nd burner ports (from left to right), you can see the wire leading to the flame sensor.The sensor is easily accessible and typically mounted by one 1/4” hex head screw. Upon removing this screw, the sensor will slide out so that you can easily clean it. Carefully remove the sensor; it may be necessary to detach the wire fixed to the end of it to get more room to work, but this is not usually necessary.
Clean the Sensor. Once you have removed the sensor, gently rub the metal rod (only) with soft steel wool or soft scotch brie type pad NEVER USE SANDPAPER as it will damage the flame rod. Remember, you are not sanding down an auto body, but simply ridding the sensor of any build up it may have. Then, use a clean paper towel to wipe clean any dust left behind .
Replace the Sensor. Once you’ve cleaned the sensor, simply reconnect the wire if you’ve taken it off, remount the sensor to the burner assembly using the 1/4” screw, replace the door(s) on the unit, and turn the power back on.
Check Your Results. If the unit takes a few extra seconds to start up or the fan immediately kicks on and runs for a bit, this is normal. Shutting down the power to the unit can cause it to reset and run through a short series of checks before trying to fire again. Once this check is complete, the unit should begin to operate by command of the thermostat. Make sure the unit re-fires and runs properly until the thermostat is satisfied, at least once before being confident your problem is solved.
How to Replace a Broken Flame Sensor. If cleaning your flame sensor did not work, it’s possible that the sensor is broken and that the furnace is operating as it should. You may need to replace the sensor, in which case you can follow these same instructions with the exception that no sanding is involved; just remove one sensor and replace it with a new sensor. Of course something else could be causing the problem and at this point, you should contact a service repair technician.
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