Ignition lockout
A state a gas appliance control enters after a set number of unsuccessful attempts to establish and prove a flame. The control stops offering heat rather than continuing to try, and it either waits a published interval before retrying or requires somebody to reset it.
Also called lockout, hard lockout
What is an ignition lockout?
An ignition lockout is a gas control refusing further attempts after a set number of failed trials for ignition. Some controls release the lockout after a published interval; others require a manual reset before heat is offered again.
Ignition lockout: how it works
Each attempt to light is a trial: purge, igniter warm-up, gas admission, and flame proving within a fixed window. A failed trial increments a counter, and reaching the limit puts the control into lockout. The counter exists because a single failure can be transient, while several in succession indicate a condition that will not resolve by repetition.
Where you meet the term
- On a furnace that heats overnight, fails in the evening, and works again the following morning without anyone attending it.
- In a code table where one number records a failed trial and a different number records the lockout that follows several of them.
- On a boiler control panel with a reset button that only appears to work while the underlying condition is absent.
How to check it
- Record when it locked out and when heat returned. A gap matching the published release interval indicates a timed reset rather than anything changing, which is one of the most misread patterns in domestic heating. Owner check
- Note whether any flame was heard before the lockout. Attempts that produce a brief flame point at proving, while attempts that produce none point at ignition or gas supply, and both end in the same lockout. Owner check
- Measure the flame signal and the working gas pressure. The proving signal in microamps and the pressure at the appliance under load are the two numbers that separate the candidate causes behind a repeated lockout. Technician
Ignition lockout: what it is not
- A lockout releasing on its own is not a repair. Where the control publishes a timed release, heat returning after that interval says nothing about whether the cause is still present.
- A lockout is not the same as a single failed ignition. One records that the control has given up, and the other records one unsuccessful attempt while retries continue.
Ignition lockout questions
How many times will a furnace try to light?
The number is published per control. Carrier states four consecutive unsuccessful trials for the two-stage control documented in its troubleshooting guide, with an automatic reset after three hours.
Is it safe to keep resetting a lockout?
Each reset spends a further set of ignition attempts against an unchanged condition. One reset establishes whether the fault repeats; beyond that the practice adds risk without adding information.
Why does heating come back by itself in the morning?
Controls with a timed release offer heat again once the interval expires. Whether the attempts then succeed depends on conditions that may have shifted slightly rather than on anything having been fixed.
Where this definition comes from
Written from service manual, manufacturer support article material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- Deluxe 2-Stage Gas-Fired Induced-Combustion Furnaces With PSC or ICM Blower Motor Troubleshooting Guide (58-3T)Carrier troubleshooting guide for deluxe two-stage gas-fired induced-combustion furnaces with PSC or ICM blower motors. Its status code index reads 11 no previous code, 12 blower on after power up, 13 limit or flame rollout switch lockout, 14 ignition lockout, 21 gas heating lockout, 22 abnormal flame-proving signal, 23 low-heat pressure switch did not open, 24 secondary voltage fuse is open, 31 high-heat pressure switch or relay did not close or reopened, 32 low-heat pressure, draft safeguard, or auxiliary limit switch did not close or reopened, 33 limit or flame rollout switch is open, 34 ignition-proving fault, 43 low-heat pressure, draft safeguard, or auxiliary limit switch open while the high-heat pressure switch is closed, and 45 replace control. The schematic notes state that ignition lockout occurs after four consecutive unsuccessful trials for ignition and that the control resets automatically after three hours, that fuse FU1 is a 3 amp automotive blade type to be replaced only with a 3 amp fuse, and that blower-on delay is 45 seconds for gas heating and 2 seconds for cooling or heat pump operation.
- Gas furnace technical frequently asked questionsRheem gas furnace technical FAQ: improper phasing or polarity and a dirty flame sense rod both preventing flame rectification, incorrect manifold gas pressure as a cause of failed flame sense, four ignition trials with a one-blink code reported after four failed trials or four flame failures in one call for heat, reset by removing the 115 volt supply or switching the thermostat off for five to ten seconds, the main limit opening on low airflow across the heat exchanger or excessive manifold gas pressure, and a pressure switch failing to close on a blocked vent, a damaged heat exchanger, or an induced draft blower not running to speed.