What furnace short cycling looks like
The burners may light for a few minutes and shut off before the thermostat is satisfied.
The blower may continue while the burners cycle on and off.
Airflow and overheating
Dirty filters, closed registers, undersized ducts, dirty blower wheels, and incorrect fan speed can cause high temperature rise.
The limit switch opens to protect the furnace.
Ignition and flame problems
Weak flame signal, gas pressure, venting, pressure-switch, or condensate issues can interrupt burner operation.
Error codes often help identify the safety circuit involved.
Thermostat and controls
A thermostat near a heat source, damaged wiring, or an oversized furnace can create short cycles.
Control-board faults are possible but should not be assumed first.
Diagnosis and repair
Technicians measure temperature rise, static pressure, flame signal, gas pressure, and venting performance.
The repair should address the cause of the safety trip.
Frequently asked questions
Can a dirty filter cause it?
Yes.
Can oversized equipment cause it?
Yes.
Is short cycling expensive?
It can waste energy and increase wear.
Can I keep running it?
Repeated overheating or ignition failures should be evaluated.
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