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SECTION 1
DESIGN PRINCIPLES AND OPERATING SEQUENCE
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 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
appliance 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.
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 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
ensure flame stability at the bur ner. Once
successful ignition has been achieved, the
electronic circuitry increases the gas rate to
maximum or will modulate output to stabilise the
temperature.
In the event of the appliance exceeding the desired
temperature (set point) the burner will shut down
until the temperature drops. When the request for
DHW has been satisfied the appliance pump and
fan may continue to operate to dissipate 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
temperature 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.
Return
temperature
sensor
Once
Expansion
vessel
Pump
Diverter
valve
Automatic
by-pass
Safety
valve
Fig. 2
Top AAV
Flow temperature
Main heat
exchanger
Bottom
DHW heat
AAV
exchanger
Pressure
switch
DHW
non return
valve
Drain
valve
CH
CH
DHW
return
flow
outlet
sensor
DHW
temperature
sensor
Flow
regulator
DHW flow
switch
DHW
inlet
3
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