If your gas furnace is suddenly shutting off almost as soon as it turns on, it has a condition known as short cycling. If your furnace short cycles, it may not warm your house very well. It might also trigger a safety mechanism that turns the furnace off completely.

A few things can cause your furnace to shut off too soon, and a common reason is a problem with the flame sensor. Here's a look at what the flame sensor does and the heating repairs that may be needed when it causes your furnace to short cycle.

The Flame Sensor's Job Is To Shut The Furnace Off

The flame sensor is in your furnace to detect flames, and if flames aren't detected, the sensor is supposed to shut the furnace off. So, when the flame sensor makes the furnace short cycle, it could just be doing its job since you don't want a gas furnace to not light a flame or gas could build inside. However, the flame sensor can malfunction too, and then it needs to be cleaned or replaced.

A Dirty Flame Sensor Can't Detect Flames

Dealing with a dirty flame sensor is a common heating repair. Soot and corrosion can build up on the sensor rod over time. When that happens, the sensor can't detect the flames properly. In many cases, the sensor can be removed and cleaned carefully to get rid of the built-up debris. This might require scrubbing the rod to get rid of corrosion. The sensor can sometimes be cleaned while it's in place, but if the heating repair technician can't reach it well enough, the sensor can be removed.

Once the sensor is clean, the heating repair technician can put it back in and test it to make sure the furnace doesn't short cycle any longer.

A Broken Flame Sensor Is Fairly Easy To Replace

If the end of the sensor is cracked or broken, the technician has to remove the old sensor by unscrewing it from the furnace and pulling it out. The technician may test it with a multimeter first to verify the part is bad. Then a new sensor can be inserted and tightened with a screw. Changing a flame sensor is an easy heating repair as long as there is plenty of room to work with the parts in a tight space.  

While flame sensor problems are a common reason for furnace short cycling, there might be a different cause. Don't delay calling a heating repair company when your furnace is short cycling because your furnace might be damaged. The heating technician can troubleshoot the issue and pinpoint the problem so repairs can be done quickly.