281 Issue 1 - Service Manual - BX3
14
3.10 Operation Flow Charts
Heater “Start up” Flow Chart
Combustion fan hold off (2 sec)
Call from heat from the thermostat
Combustion Fan Prepurge (20 sec)
Ignition
Initiate main fan hold-off time of 20
seconds.
Fan speed ramps up to required
speed
Steady state operation
Flame detect time
Has flame been
detected within 5
seconds?
Ignition retry phase activated
(5 Max number of Ignition
attempts)
No
No
Flame validate time
Has flame been present
for 5.5 seconds?
Yes
Pressure Switch Closes
Normal operation continues
System checks:
Flame sensors earth
Pressure switch open
