1104UESAGBEN, page 20/31
This heater is equipped with a direct spark multi tray burner control relay. The con-
trol relay monitors the safety devices and controls the operation of the venter motor
and the gas valve between heat cycles.
The time line below illustrates a normal heat cycle.
De
fi
nitions
Start position:
The system is not in lock-out position and can proceed with the start-up sequence upon a demand for
heat.
Pre-purge time: This is a period of 20 seconds during which the combustion fan (venter) operates prior to activation of the
ignition
device.
Safety time:
The safety time is the delay between the gas valve being energised and the
fl
ame sensor checking for the
presence of a
fl
ame. This is a period of 5 seconds.
Note:
If
no
fl
ame is sensed, the burner relay will attempt ignition 5 times before going into lock-out mode.
Post-purge time: This is the time of 10 seconds between burner shut-down and the moment the combustion fan (venter) is
de-energized.
Start pre-purge
Energisation of venter motor.
If the differential pressure switch
is in normally closed position
(start position).
Power to gas valve and ignitor
Sensor checks for the presence of a flame
End of heat demand.
De-energisation of gas valve.
De-energisation of venter motor
First heat demand signal.
Check on pressure switch.
Must be in closed or start position.
If not, there will be no power to
the venter motor.
The power to the burner relay is off
until the pressure switch goes to
normally closed - or start position.
Safety check on flame sensor.
If there is a flame, the relay will
go to lock-out. The light in the red reset
switch, mounted visibly on the heater
will glow.
Line output during ignition time to control
high fire start on two stage or modulation
applications.
If no flame, then repeat starting
at pre-purge for 5 attempts.
If no ionisation after 5 attempts, then
lock-out.
Pre-purge
time
Ignition
time=
Safety
time
Normal operation
of burner relay
Post-purge time
20 sec
5 sec
10 sec
time
Start position
9. IGNITION SYSTEM
