You can fix this
Likely cause: the thermostat is reading false heat
A thermostat in the sun, by a supply vent, or near a lamp or TV warms up faster than the room and shuts the furnace off early.
Why this happens
Bryant lists thermostat placement among the causes of short cycling, and Carrier and Trane list the thermostat too. When warm air or sunlight hits the thermostat, it thinks the room has reached the set temperature and ends the cycle. Moving a thermostat means rewiring it, which is a job for a technician.
How to fix it
- Close blinds or curtains that let sun hit the thermostat.
- Move lamps, TVs or other heat sources away from it.
- If a supply vent blows at it, redirect the vent's louvers away from the thermostat. Don't close the vent.
- Time the next few cycles. If they get longer, that was the problem.
- If the thermostat simply sits in a bad spot, ask an HVAC technician about relocating it. Don't move the wiring yourself.
When to stop. If cycles stay short after you've removed the heat source, turn the heat off and call an HVAC technician.
If this does not fix it, tell the HVAC technician
- Where the thermostat is and what was near it.
- How long cycles lasted before and after you blocked the heat source.
- The thermostat brand and model.
Build the full list: what to tell the HVAC technician.
Start this troubleshooter over
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