HVAC Q&A: Furnace Ignitor

Q:  My furnace ignitor lights and the heat turns on, however, it stops shortly after. How can I resolve this issue? 

A:  It is likely that such behaviour is caused by a malfunctioning flame sensor. A flame sensor is a rather simple device located at the burner assembly — in front of the flame stream inside the furnace. The purpose of this component is part of a safety circuit as it is to indicate the presence of a flame when the gas valve is open and to shut off the unit if no flame is detected. If the flames go out and the furnace continues to emit gas with nothing to ignite it, a dangerous buildup of unburned gas in the area around the furnace will potentially occur. 

More often than not, a flame sensor is not broken but dirty from oxidation deposits. Because of the low tolerance a flame sensor has for variations in its reading, the slightest coating of oxides will cause the furnace unit to shut down. Most service work regarding furnaces can be complicated, requiring the skills of an HVAC professional. However, cleaning a flame sensor can be quite a simple process that you can undertake yourself and it often resolves such issues. 

To do this, you first want to make sure you shut off the power to the furnace. There is often a toggle switch mounted on or near the furnace unit. The sensor may be easy to access and can be removed by unscrewing it. Once it is removed, you can clean it by gently rubbing it with sandpaper. Remount the sensor on the burner assembly and turn the power back on. (Remember, shutting off the power may cause the furnace to reset and run through a brief series of checks before trying to fire again) If you have trouble locating any of the parts just discussed, it is best to refer to your furnace manual on the manufacturer’s website.

If this process did not solve your problem, double check to see that your furnace filter is free of dust and replace it for a new filter if that is not the case. 

You can suspect an internal malfunction of some kind in the furnace controls or clogged burners if your furnace continues to shut off even after these two procedures —for which our HVAC technicians should be contacted.

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