Troubleshooting a gas furnace
On. Off. On again.
On a very cold night, a furnace cycling often can be normal. Day and night in mild weather, it isn't.
Before you call anyone
Short cycling: check, understand, then call
A short-cycling furnace isn't usually dangerous, but it wears parts and costs money. Start with the cheap causes.
Safe to check yourself
Check these first
From Trane's and Carrier's advice to owners.
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Source: Carrier, Common Thermostat Issues, checked 2026-10-22.
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Source: Trane, Furnace Short Cycling, checked 2026-10-22.
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Source: Trane, Furnace Short Cycling, checked 2026-10-22.
Worth a visit from us
What it usually means
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A furnace too big for the house
Trane calls an oversized furnace the most common cause. If it has short cycled since the day it was installed, it may have been sized wrong.
What we do: We'll tell you plainly if it's the furnace's size, and what a right-sized one involves.
Source: Trane, Furnace Short Cycling, checked 2026-10-22.
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A faulty limit switch
It thinks the furnace is overheating and shuts it down early.
What we do: We test the switch and replace it if it's at fault.
Source: Trane, Furnace Short Cycling, checked 2026-10-22.
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A cracked heat exchanger
It can overheat the furnace and shut it down. Heat exchangers are meant to last the furnace's life, so on an older one this is a repair-or-replace talk.
What we do: We inspect it and show you what we find before you decide.
Source: Trane, Furnace Short Cycling, checked 2026-10-22.
Stop, and call
When to call
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Cycling day and night in mild weather
That's abnormal. Trane doesn't call it dangerous, but it costs you in bills and repairs, so get the cause found.
Source: Trane, Furnace Short Cycling, checked 2026-10-22.
Tell us what it's doing. We'll take it from there.
Call and describe the problem: the noise, the smell, the room that never warms up. Or book a visit online.
