Your furnace runs for a couple minutes, shuts off, waits, runs again, shuts off. Over and over. It's noisy and it's burning out parts.
You probably came here because…
- Furnace kicks on and off every 2-5 minutes
- The house never actually reaches the set temperature
- You hear the ignition sequence multiple times per hour
- Utility bill higher than expected even though the house feels cold
What’s actually happening
Short-cycling has three main causes: an oversized furnace (installed too big for the house), a clogged filter or blocked airflow (system overheats and safety-trips), or a bad flame sensor or thermostat that keeps losing signal.
The oversized-furnace problem is common in older homes that got a 'bigger is better' furnace installed 15 years ago. It heats the air near the thermostat too fast, satisfies the call, shuts off, then cold air from the rest of the house reaches the thermostat and it starts over.
Short-cycling doubles or triples your ignitor wear, stresses the heat exchanger, and burns more gas than a steady long cycle. Fix it soon.
What we do about it
Change the filter
Clogged filters restrict airflow, heat exchangers overheat, safety switch trips, furnace shuts off. New filter is a $10 test that fixes this in a lot of homes.
Check thermostat placement
If your thermostat is in direct sunlight, near a supply vent, or on an exterior wall, it's getting bad readings. That'll cause short-cycling by itself.
Clean the flame sensor
The flame sensor is a small metal rod in the burner assembly. It gets coated with soot and stops sensing the flame properly, so the furnace shuts the gas off within seconds. Cleaning it with fine sandpaper takes 10 minutes and often solves it. If you're not comfortable pulling it, we'll do it.
When to just call
If the furnace is genuinely oversized, the only permanent fix is a right-sized replacement – but a lot of times it's the flame sensor or a bad thermostat first. Get us to test before you assume you need a new furnace. Call (423) 637-1846.
Ready to fix it?
Call the family that’s been doing this in the Sequatchie Valley since 1996.