6
1.1 PRINCIPLE COMPONENTS
•
A fully integrated electronic control board featuring electronic
temperature control, anti-cycle control, pump over-run, self
diagnostic fault indicator
•
Heat exchanger
•
Electronic ignition with flame supervision
•
Pump
•
Fan
•
Expansion vessel
•
Water pressure switch
•
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, if the primary
temperature falls to 5°C, the appliance will function on
minimum power until the temperature on main reaches
35°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 (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 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 tem-
perature 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 fan is started, the air pressure switch will give the signal
voltage to 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.
SECTION 1 - DESIGN PRINCIPLES AND OPERATING SEQUENCE
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;
•
air pressure switch 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 safety valve which releases excess pressure from the
primary circuit.
Fig. 4
Expansion
vessel
Safety
valve
Pump
Heat
exchanger
Bottom
AAV
Pressure
switch
Drain
valve
Automatic
by-pass
CH
return
CH
flow
DHW
inlet
DHW
outlet
DHW
flow
switch
Secondary
thermistor
Primary
thermistor