How to Reset a Furnace: Which Reset, and When Not To

Reset the control board

Power off and on. Use the switch on or near the furnace, or its breaker. White-Rodgers says the 50M56X resets with its 24 volt power off for more than 10 seconds, and the 21V51U with 20 seconds or longer. Resideo gives more than 10 seconds for the S9200.

The thermostat. Turn it down so the call for heat stops, then back up. Resideo says more than 5 seconds but less than 20 for the S9200, and White-Rodgers between one and 20 seconds for the 21V51U. Goodman says 1 to 20 seconds.

Wait. Many boards try again by themselves after an hour: White-Rodgers’ 50M56X, 21V51U and 50M56U, and Goodman and York all say so. ICP’s ignition and limit lockouts wait three hours. Rheem shows 10 on the display during its one hour lockout.

The exception. White-Rodgers says a thermostat reset does not work if flame was sensed with the gas valve off.

Know the switch first

The rollout switch. Down by the burners, often with a small red button. ICP and York both say it needs a manual reset, and York says to check the combustion air, the inducer, the heat exchanger and the burners first.

The limit switch. Higher up, on the cabinet. Most reset themselves when things cool down. On the manual kind, one press is a test, and a second is feeding a fault: why a furnace overheats and cuts out.

A hard lockout. Resideo says the S9200’s rollout and gas valve relay lockouts need a power cycle, and that after a rollout the furnace must not run until the repair is made.

Reset once, then stop

Once. If a reset clears it and the furnace runs normally, it may have been a one off.

The same code again. Stop resetting. ICP’s advice for its steady light lockout is to reset the power, and to replace the control if the code repeats. The code names the part to look at: why a furnace will not light.

A lockout after failed lighting. Check the gas is on at the furnace, and on propane that the tank has gas, before any second reset.

One press of the burner reset

The button on the burner. Oil burners have a control with a reset button. One press, and only with no smell of oil or smoke.

Beckett GeniSys. Beckett says a flashing red light is a soft lockout one short click clears, and a steady red light is a hard lockout for a technician: the Beckett lights.

Honeywell R7184. Resideo limits its resets, and restricted mode takes a 30 second hold that belongs with the technician: the R7184 light and reset.