When the furnace starts and shuts off after about 20-30 seconds, there is likely a problem with the proving of flame. When a furnace starts, it checks that the combustible gas is properly lit to avoid flooding the home with unlit gases and causing damage to the unit in the form of soot.
You may notice that there will be flames and then the unit shuts off after 20-30 seconds. If the problem is caused due to the gas delivery to the burners, then you may see no flames at all and the furnace shuts off after 20-30 seconds.
| Code | Meaning | Potential issues |
| Constant ON | – | Control has 24VAC power rapid |
| RAPID FLASHING | Line voltage (115VAC) polarity reversed | If twinned, refer to twinning kit instructions. |
| 1 blink | NO PREVIOUS CODE | Stored status codes are erased when power (115VAC or 24VAC) to control is interrupted or 48 hours after each fault is cleared. |
| 2 blinks |
BLOWER ON AFTER POWER UP (115VAC |
The blower runs for 90 seconds if the unit is powered up during a call for heat (R-W closed) |
| 3 blinks | LIMIT OR FLAME ROLL-OUT SWITCH LOCKOUT | Control will auto-reset after 3 hours. Reset the switch or replace the fuse link. |
| 4 blinks | IGNITION LOCKOUT | Control will auto-reset after 3 hours. |
| 2-1 blinks | GAS HEATING LOCKOUT | Control won’t auto-reset. Check for either a badly-wired gas valve or a defective control. |
| 2-2 blinks | ABNORMAL FLAME- PROVING SIGNAL | Flame is proved while the gas valve is de-energized. Check for either a leaky or stuck-open gas valve. |
| 2-3 blinks | THE PRESSURE SWITCH DIDN’T OPEN | Check for an obstruction in the pressure tubing or a pressure switch that is stuck closed. |
| 2-4 blinks | THE SECONDARY VOLTAGE FUSE IS OPEN | Check for a short circuit in the secondary voltage wiring. |
| 3-1 blinks | PRESSURE, DRAFT SAFEGUARD, AUX- LIMIT SWITCH DIDN’T CLOSE (OR REOPENED, DOWNFLOW ONLY) | If open for longer than 5 minutes, the inducer will shut off for 15 minutes before retry. Check for: low inducer voltage; proper vent sizing; defective inducer motor; defective blower motor or capacitor; defective pressure switch; restricted vent; excessive wind, inadequate combustion air supply; or obstructed pressure tubing. |
| 3-3 blinks | LIMIT OR FLAME ROLL-OUT SWITCH IS OPEN | If the switch is open for longer than 3 minutes, the code will change to #1-3. The flame roll-out switch requires a manual reset. Check for: defective blower motor or capacitor; dirty filter or restricted duct system; loose blower wheel; faulty switch or connections; or inadequate combustion air supply. |
| 3-4 blinks | IGNITION PROVING FAILURE | Control will try three more times before lockout #1-4 will occur. If the flame signal is lost after the trial for the ignition period, the blower will come on for a 90-second recycle delay. Check for: build-up on the flame sensor; proper microamp distribution to the flame sensor; defective gas valve or turned off gas valve; faulty hot surface ignitor; low inlet gas pressure; the manual valve is shut off; continuity of control ground; low flame carryover or rough ignition; ungrounded flame sensor. |
