2
SECTION 1
DESIGN PRINCIPLES AND OPERATING SEQUENCE
Fig. 2
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:
•
2-stage frost-protection system: the frost-pro-
tection system protects the appliance against
the risk of frost damage. The first stage enables
activation of the pump should the temperature of
the appliance fall to 7°C. The second stage
becomes active when the temperature has
dropped to 3°C. Should the second stage be-
come active, the appliance will function on
minimum power until it reaches 30°C.
•
Anti-block function: the anti-block function ena-
bles the pump to be energised for short periods,
when the appliance has been inactive for more
than 19-hours.
1.3
MODE OF OPERATION
When there is a request for heat and/or hot water,
via the programmer/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 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 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
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.
•
fan speed sensor and pressure differential mecha-
nism 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
•
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.
ECONOMY/COMFORT MODES
The boiler can be used in either comfort or
economy mode. When the economy mode has
been selected, the automatic temperature control
(SARA) functions over a reduced temperature
range. When the comfort mode is selected, the
SARA function is active throughout the entire tem-
perature range.
CH
flow
CH
return
safety
valve
expansion
vessel
pump
return
temperature
sensor
top AAV
flow
temperature
sensor
main heat
exchanger
water
pressure sensor
& gauge
bottom
AAV
transducer
automatic
by-pass