3
1.1 PRINCIPLE COMPONENTS
●
A fully integrated electronic control board featuring
electronic temperature control, anti-cycle control,
pump over-run, self-diagnostic fault indicator, full air/
gas modulation.
●
Radial aluminium heat exchanger.
●
Electronic ignition with fl ame supervision
●
Fan
●
Condensate level sensor.
1.2 MODE OF OPERATION (at rest)
When the appliance is at rest and there are no requests
for heating or hot water, the following functions are active:
●
2-stage frost-protection system – the frost-protection
system protects the appliance against the risk of frost
damage. The fi rst stage enables activation of the pump
should the temperature of the appliance fall to 6
o
C.
Should the fi rst stage become active, the appliance
will function on m25% power until it reaches
35
o
C.
●
Anti-block function – the anti-block function enables
the pump to be energised for short periods, when the
appliance has been inactive for more than 24-hours.
1.3 MODE OF OPERATION
When there is a request for heat and/or hot water, via the
programmer/time clock and/or any external control, the
pump and fan are started, the fan speed will modulate
until the correct signal voltage is received at the control
PCB. At this point an ignition sequence is enabled.
Ignition is sensed by the electronic circuitry to ensure
fl ame stability at the burner. Once successful ignition
has been achieved, the electronic circuitry increases the
gas rate to 75% for a period of 15 minutes. Thereafter,
the boiler’s output will either be increase to maximum or
modulate to suit the set requirement.
When the appliance reaches the desired temperature
the burner will shut down and the boiler will perform a
three-minute anti-cycle (timer delay).
When the request for heat has been satisfi ed the pump
and fan may continue to operate to dissipate any residual
heat within the appliance.
NOTES
●
The pump must be connected directly to the desig-
nated terminals within the appliance controls panel.
●
When power is restored to the PCB and/or the PCB
is powered for the fi rst time, the appliance will enter
a 2-minute purge cycle whereby only the pump will
run for 15-seconds then off for 15-seconds.
1.4 SAFETY DEVICES
When the appliance is in use, safe operation is ensured by:
●
Fan speed sensor and pressure differential mecha-
nism to ensure safe operation of the burner
●
A high limit thermostat that over-rides the temperature
control circuit to prevent or interrupt the operation of
the burner.
●
Flame sensor that will shut down the burner when
no fl ame signal is detected.
●
A sensor that interrupts the operation of the appliance
if the condense pipe becomes blocked.
SECTION 1 DESIGN PRINCIPLES AND OPERATING SEQUENCE
Fig. 2
CH
return
CH
fl ow
return tem-
perature
sensor
main heat
exchanger
fl ow tempera-
ture sensor
top
AAV
water/air
separator
drain
valve
