Supplied By www.heating spares.co Tel. 0161 620 6677
2
SECTION 1
DESIGN PRINCIPLES AND OPERATING SEQUENCE
Fig. 2
1.1
PRINCIPLE COMPONENTS
●
A fully integrated electronic control board fea-
turing electronic temperature control, anti-cy-
cle control, pump over-run, LED fault indicator,
full gas modulation.
●
Low-water-content, copper heat exchanger.
●
Electronic ignition with flame supervision.
●
Integral high-head pump.
●
Fan.
●
Air pressure switch.
●
Expansion vessel.
●
Water pressure switch.
●
Two-stage gas valve.
●
Pressure gauge.
●
Safety valve.
●
Condense switch.
1.2
MODE OF OPERATION (at rest)
When the appliance is at rest and there are no
requests for heating or DHW, the following func-
tions are active:
●
Frost-protection system - the frost-protection
system protects the appliance against the risk
of frost damage. Should the temperature of the
appliance fall to 5 °C, the boiler will function in
the heating mode at minimum power until it
reaches 35 °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 19-
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 will then prove the air pressure
switch. At this point an ignition sequence is
enabled.
Ignition is sensed by the electronic circuitry 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 tem-
perature the burner will shut down and the boiler
will perform a three-minute anti-cycle (timer de-
lay).
When the request for heat has been satisfied the
appliance pump and fan may continue to operate
to dissipate any residual heat within the appli-
ance.
1.4
MODE OF OPERATION (DHW)
When there is a request for DHW via a hot water
outlet or tap, the pump and fan are started, the fan
will then prove the air pressure switch. At this
point an ignition sequence is enabled.
Ignition is sensed by the electronic circuitry to
ensure flame stability at the burner. Once suc-
cessful 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 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 appli-
ance.
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 pres-
sure drop below the rated tolerance.
●
A high limit thermostat that over-rides the tem-
perature control circuit to prevent or interrupt
the operation of the burner.
●
An air pressure switch that requires the fan to
prove operation before the gas valve is ener-
gised.
●
A pressure switch that interrupts the operation
of the appliance if the condense pipe becomes
blocked.
●
A safety valve which releases excess pressure
from the primary circuit.
CH
return
CH
flow
DHW
outlet
Domestic cold
water inlet
safety valve
automatic
by-pass
diverter
valve motor
pump
AAV
expansion
vessel
latent heat
collector
flue
outlet
air
intake
pressure
switch
main heat
exchanger
CH NTC
sensor
main
burner
gas valve
DHW heat
exchanger
DHW tempera-
ture sensor
water
pressure
switch
DHW non
return valve
DHW
flow switch
