Technical data

2
SECTION 1 DESIGN PRINCIPLES AND OPERATING SEQUENCE
1.1 PRINCIPLE COMPONENTS
● A fully integrated electronic control board
featuring differential temperature control,
continuous air/gas modulation, anti-cycle
control, pump over-run, self-diagnostic fault
indicator, electronic ignition with flame
supervision & appliance frost protection
● Cast aluminium mono-block heat exchanger
● Low Nox burner with pre-mix
● Two-stage gas valve
● Pump
● Expansion vessel
● Pressure gauge
● Safety valve
1.2 MODE OF OPERATION (at rest)
When there is no demand for heating or hot water
and the appliance remains inactive for a period of
24 hours, the pump will be energised for a few
moments to prevent it from seizing. Should the
flow temperature sensor fall below 7 ºC the pump
will be energised. If the flow sensor temperature
falls to below 3 ºC the burner will be lit and the
appliance will operate at the minimum output until
the temperature of the flow sensor reaches 10 ºC,
whereupon the pump will continue to run in pump
over-run mode.
1.3 MODE OF OPERATON (heating or hot water
request)
When there is a request for heat via the time clock
and/or external controls, the pump will start and
the fan will be activated via the flow temperature
sensor. When the fan is sensed to be operating
correctly, the ignition sequence commences. The
speed of the fan and therefore the output of the
boiler is determined by the temperature of the
water sensed by the flow & return temperature
sensors, consequently a high temperature at the
flow sensor results in a lower fan speed. As the
water temperature increases, the temperature
sensors – located on the flow and return pipes of
the boiler – reduce the fan speed via the electronic
circuitry. Depending on the load, either the water
temperature will continue to rise until the set point
is achieved or the water temperature will fall
whereby fan speed will increase relative to the
output required. When the boiler has reached the
set point, the burner will switch off. The built-in
anti-cycle device prevents the burner from re-
lighting for an adjustable period of time (factory
default is 3 minutes). When the temperature of
the flow sensor falls below the set-point, the
burner will re-light.
1.4 SAFETY DEVICES
When the appliance is in use, safe operation is
ensured by:
● a high limit thermostat that interrupts the
operation of the burner;
● a differential temperature protection circuit which
interrupts the burner if the temperature
differential is inverted;
● a fan speed sensor that checks the correct
operation of the fan, thereby allowing safe
operation of the burner;
● a condense pressure switch that will stop the
burner from operating should the condense
trap become blocked;
● a safety valve which releases excess pressure
from the primary circuit.
Fig. 2
return flowgas
1
Heat
exchanger
Expansion
vessel
4
NTC1
(flow
sensor)
NTC2
(return
sensor)