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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
•
Stainless-steel heat exchanger
• Electronic ignition with flame supervision
• Integral high-head pump
• Fan
• Expansion vessel
• Water flowmeter
• Flue sensor
• Pressure transducer
• 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 5°C,
the appliance will function on minimum power until the
temperature on main reaches 35°C.
Moreover if the DHW temperature falls to 5°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 REC/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 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 burner. 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. SECTION - DESIGN PRINCIPLES AND OPERATING SEQUENCE
1.5 SAFETY DEVICES
When the appliance is in use, safe operation is ensured by:
• a pressure transducer that monitors system water pressure
and will de-activate the pump, fan, and burner should the
system water pressure drop below the required minimum
value;
• 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 and/or when incomplete combustion or
high emissions are detected;
• flue sensor that will shut down the burner if the flue threshold
temperature is exceeded;
• a safety valve which releases excess pressure from the
primary circuit.
NOTE
: when the appliance is first switched ON or when the
electrical supply is interrupted then restored, the appliance
will enter a short ‘purge’ cycle whereby the pump cycles ON &
OFF for approximately 2-minutes. Only when the ‘purge’ cycle
has been completed, will the appliance go through an ignition
sequence.
CH
return
CH
flow
DHW
outlet
DHW
inlet
DHW
flowmeter
Flow
restrictor
DHW
non-return
valve
Drain
valve
Safety
valve
Automatic
by-pass
Diverter
valve
Pressure
transducer
Pump
Analogue
pressure
gauge
Lower
AAV
Expansion
vessel
DHW heat
exchanger
DHW
temperature sensor
Return
temperature
sensor
Main heat
exchanger
AAV
High limit
thermostat
Flow
temperature
sensor
Fig. 4
