Short Cycling In Gas Furnaces: Is The Flame Sensor Faulty?

Of all the problems that can affect your home's gas furnace, short cycling can be one of the most troublesome to deal with. If your gas furnace is short cycling, it must be repaired as soon as possible.

The flame sensor is one of your furnace's simplest components, but also one of the most important. Faults with the flame sensor are one of the most common causes of short cycling in gas furnaces.

What Is Short Cycling?

A fully functioning gas furnace will continue to burn gas until your home reaches the desired temperature, as indicated on the thermostat. Short cycling occurs when the furnace deactivates itself a few seconds or minutes after activation. Without intervention, the furnace will continue to activate and deactivate itself in quick succession.

A short-cycling gas furnace will not function for long enough to adequately heat your home, leaving your home uncomfortably cold until the problem is rectified. It also wastes a lot of fuel and increases wear on your furnace's moving components (such as fan motors). 

How Can Flame Sensor Faults Cause Short Cycling?

The flame sensor is a small, metallic rod, positioned within your gas furnace's combustion chamber. It contains light sensors that detect infrared and/or ultraviolet light, both of which are produced by flames. Here are some common faults that can prevent flame sensors from functioning effectively:

Soot Buildup

Your furnace will create soot whenever it burns gas. Over time, soot deposits can build up on the surfaces of your furnace's flame sensor, covering its UV and/or IR light sensors. A thick layer of soot will prevent light from reaching the sensors, and the flame sensor will deactivate your furnace, causing short cycling. This soot will need to be removed before the furnace can be used again.

Bear in mind that gas furnaces should only produce a small amount of soot. If your furnace's flame sensor is frequently becoming caked in soot, this may indicate problems with how your furnace burns fuel. If there is water in the combustion chamber, or the chamber is not receiving enough oxygen, the furnace may produce excess soot. 

Sensor Wiring Damage

The furnace's flame sensor is connected to wiring, which sends the sensor readings to the furnace's central control board. If this wiring is damaged or corroded, the control board may not receive signals from the sensor, and it will assume that the sensor is not detecting flames.

Sensor Misalignment

For a flame sensor to function properly, its light receptors must be pointed in the right direction. If the sensor has been accidentally knocked or damaged during routine maintenance work, it may be pointing away from the combustion chamber and unable to receive light from flames. The sensor will need to be realigned or replaced if it is severely damaged.

If your gas furnace is short cycling, you should call in a professional furnace repair services as soon as possible.

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My husband spends more time out in the garage than he does in the house. He had been begging for a heating and cooling system for the garage for a few years, but until now, we couldn't afford to make the investment. Now that we have the money to buy it, I spent a lot of time trying to figure out what the most efficient way to heat and cool a garage would be. Find out what I learned here on my blog. You will learn what kind of systems to choose and what you can do to improve the efficiency of your garage.