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SECTION 1
DESIGN PRINCIPLES AND OPERATING SEQUENCE
1.1
PRINCIPLE COMPONENTS
• A fully integrated electronic control board featur-
ing electronic temperature control, anti-cycle
control, pump over-run, self-diagnostic fault in-
dicator, full air/gas modulation.
• Radial aluminium heat exchanger.
• Electronic ignition with flame supervision
• Integral high-head pump
• Fan
• Expansion vessel
• Water pressure switch
• Condensate level sensor
• Pressure gauge
• Safety valve
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:
• frost-protection system – the frost-protection
system protects the appliance against the risk
of frost damage both for CH and DHW. For CH
line, if the main temperature falls to 6°C, the
appliance will function on minimum power until
the temperature on main reaches 35°C.
Moreover if the DHW temperature falls to 4°C,
the appliance will function on minimum power
until the temperature on main reaches 55°C.
• anti-block function – the anti-block function
enables the pump and divertor valve actuator to
be energised for short periods, when the appli-
ance has been inactive for more than 24-hours.
1.3
MODE OF OPERATION (Heating)
When there is a request for heat via the 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 circuit to
ensure flame stability at the burner. Once suc-
cessful 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 tempera-
ture the burner will shut down and the boiler will
perform a three-minute anti-cycle (timer delay).
When the request for heat has been satisfied the
appliance pump and fan may continue to operate
to dissipate any residual heat within the appliance.
1.4
MODE OF OPERATION (Hot water)
When there is a request for DHW via a hot water
outlet or tap, 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 circuit to en-
sure flame stability at the burner. Once success-
ful ignition has been achieved, the electronic cir-
cuitry increases the gas rate to maximum or will
modulate output to stabilise the temperature.
In the event of the appliance exceeding the de-
sired temperature (set point) the burner will shut
down until the temperature drops. When the re-
quest for DHW has been satisfied the appliance
pump and fan may continue to operate to dissi-
pate any residual heat within the appliance.
1.5
SAFETY DEVICES
When the appliance is in use, safe operation is
ensured by:
• a water pressure switch that monitors system
water pressure and will de-activate the pump,
fan, and burner should the system water pressure
drop below the rated tolerance;
• fan speed sensor to ensure safe operation of the
burner;
• a high limit thermostat that over-rides the tem-
perature control circuit to prevent or interrupt the
operation of the burner;
• flame sensor that will shut down the burner when
no flame signal is detected;
• a sensor that interrupts the operation of the
appliance if the condense pipe becomes blocked;
• a safety valve which releases excess pressure
from the primary circuit.
Main heat
exchanger
return
temperature
sensor
DHW
temperature
sensor
DHW non
return valve
water
pressure
switch
automatic
by-pass
safety valve
CH
DHW
flow
outlet
Fig. 2
flow
temperature
sensor
Top AAV
expansion
vessel
Bottom
AAV
DHW heat
exchanger
pump
diverter
valve motor
DHW
flow switch
CH
Domestic cold
return
water inlet
3
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