Furnace short cycling
Starts, runs briefly, shuts off, repeats. Ranked from 1,600 repairs on furnaces with this symptom — and the first thing to rule out costs nothing.
Before you start — Kill the power before you touch anything gas · electrical safety
Switch the furnace off at the service switch AND at the breaker before opening the cabinet. A furnace that short cycles on a limit switch is telling you it is overheating — find out why rather than replacing the limit that is protecting it. Heat-exchanger inspection is licensed-tech work.
If you smell gas, or if the furnace short cycles with a burnt or acrid smell: stop, leave the building and call your gas utility from outside.
Narrow it down
Most likely parts ranked from 1,600 repairs
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Also check — 34%34% of matching repairs
A marginal flame sensor proves flame just long enough to run, then drops out — which reads as short cycling rather than a hard lockout.
Try this first: Clean the rod first — emery cloth, 5 minutes, free.
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Also check — 22%22% of matching repairs
An intermittent pressure switch — or a flue that is partly blocked — opens mid-cycle and shuts the burners down.
Try this first: Free: clear the switch hose of water and check the flue termination outside for snow, nests or debris.
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Also check — 18%18% of matching repairs
A furnace tripping its limit is overheating, and the usual cause is airflow, not the limit. Replace the limit only once you know why it opened.
Try this first: Change the filter and open every supply register first. A clogged filter is the most common cause of limit-trip short cycling, and it is a $10 fix.
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Also check — 12%
CTB-1084
Integrated Furnace Control Board
23 in stock · ships today
$128.00 Pro price $108.80 save $19.20 (15%)12% of matching repairsA board that loses flame sense or mis-times the sequence cycles the furnace. Test the cheap parts first — this is the expensive guess.
Try this first: Read the diagnostic flash code through the door window first.
The remaining 14% of matching repairs resolved without a replacement part — a filter, a reset or a thermostat setting.
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Ask a tech — freeCommon questions about this symptom
My furnace runs for a few minutes then shuts off — what's wrong?
A furnace that runs several minutes and then quits is usually overheating and tripping its limit switch — and the cause is almost always airflow. Change the filter and open the supply registers first; that is a $10 fix and it resolves most of these. If it still trips, the limit switch itself (43%) or a failing blower motor (24%) is next.
See the parts for this →My furnace blower runs constantly — what's wrong?
First, check the thermostat: a fan set to ON rather than AUTO is the single most common cause and it is a free fix. If the fan is on AUTO and the blower still never stops, a limit switch stuck open (38%) or a control board failing to drop the fan relay (31%) is the likely cause.
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