Article updated on 19 February 2021.
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A furnace is something we depend on heavily both in personal and industrial settings, and it can cause a lot of difficulties when it stops working.
To avoid a lot of worries and unnecessary expenses, it is worth routinely checking the sensor within the furnace itself; like a broken sensor can also stop the furnace from working. If so, this is a problem that can be self-diagnosed and fixed.
Although it may seem like a contraption that makes life a little more complicated, the sensor is a very important piece of machinery that you shouldn't run a furnace without.
What's a Furnace Sensor?
The furnace flame sensor, or furnace sensor rod, is a thin metal rod, usually bent, located near the pilot light in a furnace. The rod itself has a very small voltage connected to a conductor, allowing the rod to monitor performance.
If the pilot flame isn't lit, the potential will remain in the rod with no current and the furnace will not allow the gas valve open. If the rod doesn't find a current, it will try again after a few seconds, but will eventually shut off for about an hour. The rod also has a piece of ceramic to insulate it and prevent grounding.
How Sensors Keep You Safe
While a lot can go wrong with your furnace, many of the causes are there as a failsafe to prevent bigger problems from occurring. The same could easily be said about the furnace sensor. While sometimes inconvenient when they suddenly stop working, they exist to keep users safe.
The whole point of the sensor is to ensure that the pilot light is on when the gas gets pumped out. If the pilot light is not on, the fire will not catch and no gas will be burned away. Instead, the furnace will remain on but fail to heat the house, and the gas will continue to pump into every available space. This could be fatal, as the gas itself can kill people or result in an explosion.
Furnace Sensor Maintenance
More often than not, issues are not actually due to a broken sensor, but due to the sensor being dirty or corroded. If that's the case, then fixing the issue is easy. As the sensor is placed so close to the pilot light, it will collect carbon deposits or dust over time. Due to its sensitivity, even the smallest amount of dust will throw the sensor off and cause it to make false readings.
While cleaning the sensor is easy, there is a process to it that you do not want to get wrong, so it is often worth calling a professional. In simple terms, you have to turn off the furnace before removing, cleaning and replacing the sensor, and then the furnace must be tested again.
How to Clean the Sensor
Before touching anything, the furnace must be switched off to avoid gas leaks or open flames while you are working with the sensor. Once the furnace is turned off, you can begin by removing the sensor.
The sensor is usually easily accessible, often mounted by a quarter-inch hex-head screw. Remove the screw and the sensor should easily slide out. In some models, you may have to remove a wire too, but this isn't always necessary.
Next, the sensor has to be cleaned. A piece of very high-grit (smoother) sandpaper, a wire brush, or steel wool are often used. Rub-down the metal rod gently to get rid of any grit or buildup. When you're done, wipe it down with a cloth or paper towel.
Once it's clean, reconnect the sensor with the same process you used to remove it. Reconnect the wires if you disconnected them, then slide the sensor back in place and re-mount the screw in the same condition you found it.
After this process, the furnace needs to be re-tested. It may run a little differently than what you're used to at first; it may take a few more seconds to come on or just run the fan for a little while. After it is reset, it should start working normally, assuming the dirty sensor was the problem in the first place.
As mentioned previously, a professional should always be consulted in any case, to ensure that the correct solution is being implemented correctly.
Sensors Are Life Savers
The furnace sensor is a necessary part of using furnaces safely. Knowing what it is and keeping it clean and maintained can help with costs and prevent faults from occurring.
So, the next time your furnace acts funny, do not panic, it is probably just keeping you safe.
Sources and Further Reading
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