Manual for LS25 - Troubleshooting and error codes + PDF Download

The heating sequence initiates when the thermostat calls for heat, activating the combustion air inducer. A pressure switch confirms inducer operation before ignition starts. Following a 30-second pre-purge, spark ignition is energized, and solenoid valves in the gas valve open. Spark ignites the gas, and a sensor verifies the flame, continuing combustion. If flame is not detected after the first trial, ignition is retried twice before a lockout, which auto-resets after 60 minutes. Burners should light smoothly with blue flames, and the fan activates 30 seconds post-ignition. Upon thermostat satisfaction, the gas valve closes, followed by the combustion air inducer after 30 seconds, and finally, the system fan de-energizes after approximately 150 seconds.