Flame rollout switch
A manual-reset safety device fitted in the burner compartment of a gas furnace. It opens when heat or flame is present outside the path combustion is meant to follow, and opening it removes the gas valve circuit so the furnace cannot fire until somebody investigates why heat reached that position.
Also called rollout switch, rollout safety
What is a flame rollout switch?
A flame rollout switch is a manual-reset safety in a gas furnace burner compartment. It opens when heat appears outside the designed combustion path, which cuts the gas valve circuit and locks the furnace out until the cause is found.
Flame rollout switch: how it works
Combustion in a healthy furnace is drawn inward through the burner ports and away through the heat exchanger. If the exchanger is restricted, cracked, or badly vented, flame and hot gas can travel back out toward the burner compartment instead. A rollout switch sits where that would happen and opens on temperature, breaking the series safety circuit the gas valve depends on.
Where you meet the term
- On a furnace code that names a limit or rollout circuit without saying which of the two devices opened.
- As a small red or black button in the burner area, which a technician may reset only after establishing why it operated.
- In a service report explaining why a heat exchanger inspection was recommended rather than a part replacement.
How to check it
- Look for soot or scorching around the burner area. Discoloration, soot marks, or melted wire insulation near the burners are visible from outside the cabinet on many furnaces and are worth photographing for the engineer. Owner check
- Establish whether combustion products are entering the room. A carbon monoxide alarm sounding, or an unfamiliar smell during firing, turns this from a service call into an evacuation and a call to the gas emergency number. Owner check
- Inspect the heat exchanger and the venting before resetting. A rollout device that has operated is reporting a combustion path problem, so the exchanger and flue are examined before the switch is reset or replaced. Technician
Flame rollout switch: what it is not
- A rollout switch is not a nuisance device to be reset until it stays in. It is a manual-reset safety precisely so that a person has to look at the furnace before it fires again.
- A rollout trip is not the same as a high-limit trip, even where one code covers both. One reports air-path temperature and the other reports flame where flame should not be.
Flame rollout switch questions
Where is the rollout switch on a furnace?
It is mounted in the burner compartment, positioned where escaping flame or hot gas would reach first. The exact location differs by model and is shown in the installation instructions for that furnace.
Why does a rollout switch need a manual reset?
An automatic reset would let the furnace fire again without anyone examining why heat reached the burner compartment. Requiring a person to intervene is the point of the device rather than an inconvenience.
Can a dirty filter trip a rollout switch?
Restricted airflow raises furnace temperatures and can contribute, but a rollout device responds to flame or heat in the burner area specifically. Treating it as a filter problem skips the combustion question it raised.
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.
- What is a furnace limit switchCarrier homeowner resource on the furnace limit switch: a bimetallic strip that opens and closes contacts controlling the blower and the gas valve, an approximate blower-on point near 130 degrees Fahrenheit, an approximate upper safety limit near 200 degrees, a fan-off point near 100 degrees, the symptoms of a constantly running blower, a furnace that will not ignite and rapid short cycling, the causes it names as dirty filters, blocked or closed vents, blower motor failure and a dirty evaporator coil, and the instruction never to bypass the switch.