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3.0 APPLIANCE OPERATION
Publication No. 5111811
NOTE: All delay timers mentioned in 3.1 and 3.2
are overridden by domestic hot water demand.
3.1 Central Heating Mode (Fig. 4)
1. With a demand for heating, the pump circulates
water through the primary circuit. At a pre-
determined flow rate the central heating flow switch
operates, initiating the ignition sequence.
2. The main burner ignites at low rate, then the gas
valve controls the gas rate to maintain the heating
temperature measured by the temperature sensor.
3. When the flow temperature exceeds the setting
temperature, a 3 minute delay occurs before the
burner relights automatically (anti-cycling). The pump
continues to run during this period.
3.2 Domestic Hot Water Mode (Fig. 5)
1. Priority is given to the domestic hot water supply.
A demand at a tap or shower will override any central
heating requirement.
2. The flow of water will operate the DHW flow switch
which causes the 3 way valve to change position.
This will allow the pump to circulate the primary water
through the DHW plate heat exchanger.
3. The burner will light automatically and the
temperature of the domestic hot water is controlled
by the temperature sensor.
4. When the domestic hot water demand ceases the
burner will extinguish and the diverter valve will
remain in the domestic hot water mode, unless there
is a demand for central heating.
IMPORTANT: When the selector switch is in the
‘0’ (Off) position the electrical supply to the boiler
is isolated. The boiler will not operate and the
integral timer (if fitted) will require resetting once
the selector switch is turned to either the DHW
or CH position.
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1 Primary Heat Exchanger
2 Burner
3 Ignition Electrode
4 Flame Sensing Electrode
5 Gas Valve
6 Pump
7 Automatic Air Vent
8 Plate Heat Exchanger
9 Flow Sensor with Filter
10 Pressure Relief Valve
11 Boiler Drain Point
12 Heating Return
13 Cold Water Inlet On/Off Valve and Filter
14 Gas Inlet
15 Domestic Hot Water Outlet
16 Heating Flow
17 Pressure Gauge
18 Hydraulic Differential Pressure Sensor Microswitch
19 Automatic By-Pass
20 Hydraulic Differential Pressure Sensor
21 Diverter Valve Assembly
22 Domestic Hot Water Flow Priority Assembly
23 Domestic Hot Water Flow Priority Microswitch
24 Temperature Sensor
25 Overheat Thermostat
26 Expansion Vessel
27 Secondary Heat Exchanger
Key
Central Heating Circuit
Domestic Hot Water Circuit
Fig. 4
Fig. 5
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