Why Does My Furnace Keep Shutting Off?
A furnace that starts and stops in short bursts is telling you something. Here are the usual causes and what to check first.
Callison Electric Heating & Cooling most often traces a furnace that keeps shutting off to a dirty filter, a thermostat issue, a blocked flue, or an overheating safety shutoff. Start with the filter, then call for a diagnosis if it continues. Call 540-294-3189.
A furnace turning on and off in short cycles is called short-cycling. It wears the system out and never properly heats the house. Here is what we check on a furnace repair call, roughly in order.
1. A dirty filter (check this first)
A clogged filter chokes airflow, the furnace overheats, and a safety switch shuts it down before it starts again. This is the single most common cause, and swapping the filter is free. Do this before anything else.
2. Thermostat problems
A thermostat placed near a heat source, with a weak battery, or wired loosely can cut the furnace off early. Sometimes the fix is as simple as fresh batteries.
3. Overheating and safety shutoffs
If the furnace runs hot, a limit switch shuts it down to protect it. That can come from restricted airflow, a failing blower, or a dirty system. This one needs a technician.
4. A blocked flue or bad flame sensor
A blocked exhaust flue or a dirty flame sensor can both trip the furnace off as a safety measure. These are common on older systems and are a straightforward repair.
No heat on a cold night? Short-cycling can leave you without heat. Callison treats no-heat calls as a priority, and emergency HVAC service is available. If your furnace is older and failing often, our guide on repairing vs. replacing applies to heating systems too. Full details on our heating and cooling page.
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Have a question about your system?
Furnace short-cycling or no heat? We find the real cause, not just the symptom. Call before noon and a crew can usually be there the same day.
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Call 540-294-3189