When the thermostat calls for heat, the 780-845 control simultaneously initiates ignition sparking and opens the pilot valve portion of the gas valve. Pilot flame recognition stops ignition sparking and opens the main valve portion of the gas valve. Pilot burner flame is continuously monitored at a synchronous frequency for the duration of the heating cycle. Should the pilot flame fail during the heating cycle, the control will shut off the main valve until the pilot flame is established. The 780-845 lockout ignition control provides 90 seconds of spark, followed by a 6 minute time delay (purge) between ignition attempts. After three tries, if no pilot flame is sensed, the control goes into a one-hour lockout period. At the end of the lockout period, if the demand for heat is still present, the unit will repeat the three tries for ignition. Identifying Your Robertshaw ICU Terminals: MV-Main valve, PV-Pilot valve, LED-Dagnostic LED, TH-24V thermostat, PV-MV: Gas valve common, TR-Transformer ground, GND-Main Burner Ground, SENSE-Internal/external sense terminal, SPARK-Spark output. During lockout, you may override the auto-system, and manually reset the unit at the thermostat. The green diagnostic LED will be on continuously for normal operation. The LED will be off for internal lockout and will flash continuously for problems external to the control (ie. not sensing flame).