Baxi BAXI COMBI INSTANT 105 HE, Installation & Servicing Instructions Manual

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3.0 Appliance Operation
7
NOTE: All delay timers mentioned in 3.1 and 3.3 are
overridden by domestic hot water demand.
3.1 Central Heating Mode (Fig. 2)
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.
4. When the demand is satisfied the burner is
extinguished and the pump continues to run for a period
of 30 minutes (Pump Overrun).
5. If there is no other demand the pre-heat function will
operate if switched on (see Section 3.2).
3.2 Domestic Hot Water - Preheat Mode
(Fig. 3)
1. With the pre-heat function switched on (pre-heat
control fully clockwise), priority is given to the
replenishment of the pre-heat store. The DHW mode
neon ( ) will flash during this function.
2. The diverter valve remains in the DHW priority
position. This allows the pump to circulate hot water to
the store and back to the primary heat exchanger via the
bypass pipe.
3. The automatic ignition sequence commences after
approximately 25 seconds and the burner will light.
4. When the store reaches the desired temperature the
burner is extinguished. The pump continues to run for a
period of 30 seconds.
5. Following a demand for domestic hot water or the
end of a central heating ON period, the pre-heat
function restarts.
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19
16 15 14 13 12
10
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11
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17
21
23
20 22
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28
26
5 6
7
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3 4
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24
18
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 Pressure Sensor Microswitch
19 Automatic By-Pass
20 Hydraulic Pressure Sensor
21 Diverter Valve Assembly
22 Domestic Hot Water Flow Priority Assembly
23 Domestic Hot Water Flow Priority Microswitch
24 Safety Thermostat
25 Central Heating Temperature Sensor
26 Expansion Vessel & Pre-Heat Store
27 Domestic Hot Water Temperature Sensor
28 Secondary Heat Exchanger
Key
Central Heating Mode
Fig. 2
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16 15 14 13 12
10
9
11
8
17
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20 22
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26
5 6
7
2
3 4
1
25
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28
Domestic Hot Water - Preheat Mode
Fig. 3