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Serving the South Puget Sound and Western Washington Areas Since 1976

Serving the South Puget Sound and Southwest Washington Areas Since 1976

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Sunset Air Blog

Short-Cycling and Its Effects on Your Furnace

Have you noticed your furnace turning itself on and off every few minutes? If so, you have a problem. That behavior is known as “short-cycling,” and it can be quite harmful to your furnace if allowed to continue for any length of time. If you notice your furnace short-cycling, you should turn it off and call for a professional to look at it. If you’re interested in preventing it from happening in the first place (and you should be) then read on. Let’s examine the primary cause of short-cycling, and what it can do to your furnace.

Clogged Air Filter

Every furnace has an air filter installed in the return duct of the air handler. This filter is designed to protect the furnace by capturing any dust or other particles that might otherwise damage the system. Though the air filter is quite good at this job, it can become clogged with these particles if it’s not cleaned or replaced every few months. If that happens, it will restrict the flow of air into the furnace.

When the air flow into the furnace becomes obstructed, the temperature inside the system rises. Eventually, the furnace will overheat. This activates the limit switch, which shuts down the furnace as a safety measure to prevent it from damaging itself. Unfortunately, the limit switch cannot address the cause of the overheating. As soon as the furnace restarts, the clogged air filter will cause it to overheat again and the limit switch will cause it to shut down again.


The startup process is the most stressful part of the entire furnace cycle. It is during that time that the furnace attempts to reach the target temperature as quickly as possible. After the temperature is reached, it eases off and only makes the occasional adjustment to maintain the climate. When the furnace becomes locked in an endless startup process, it is put under far more stress than it was designed to handle. This can cause the heat exchanger to rapidly wear out and develop cracks, requiring replacement. The entire system will be put at greater risk for a breakdown, and its lifespan will be drastically reduced.

If you suspect your furnace of needing repairs, call Sunset Air. We provide furnace repairs throughout Olympia, WA. 

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