Page No 30 of 56 Reznor, RHC21 4000 Installation EN May 2021 D301334 Issue 0
Start position
The system is not in lock-out and can proceed with the start up sequence upon a
demand for heat
Pre-purge time
This is a period of 35 seconds during which the combustion fan operates prior to
activation of the ignition device.
Safety time
The safety time is the delay between the gas valve being energised and the flame
sensor checking for the presence of a flame. This is a period of 4 seconds.
Note : if no flame is sensed, the burner controller will attempt ignition 3 times before
going into lock-out mode.
Post-purge time
This is the time of 255 seconds between burner shut-down and the moment the
combustion fan is de-energised.
Figure 8 Ignition system timetable
