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Boiler Primary Circuit
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17
13
15
14
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Key
1
Heat Exchanger
2
Burner
3
Ignition Electrode
4
Flame Sensing Electrode
5
Gas Valve
6
Pump
7
Automatic Air Vent
8
Pressure Relief Valve
9
Boiler Drain Point
10
Gas Inlet
11
Boiler Flow
12
Boiler Return
13
Pressure Gauge
14
Automatic By-Pass
15
Hydraulic Differential Pressure Sensor
16
Safety Thermostat
17
Temperature Sensor
18
Expansion Vessel
19
Temperature Sensor
20
Secondary Heat Exchanger
© Baxi Heating UK Ltd 2007
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2
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3.0 Appliance Operation
3.1
Operating Mode (Fig. 2)
1. With a demand for heating, the pump circulates water
through the primary circuit. At a pre-determined flow rate
the hydraulic differential pressure switch operates, initiating
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the ignition sequence.
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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.
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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 3 minutes
(Pump Overrun).
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IMPORTANT: When the selector switch is in the '0'
(Off) position the electrical supply to the boiler is
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isolated. The boiler will not operate.
3.2
Frost Protection Mode
1. The frost protection mode is integral to the appliance and
functions when the selector switch (see Section 2.1) is in the
ON position (
5° C then the boiler will fire on its minimum setting until a
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flow temperature of 30° C is reached. Further protection
can be incorporated by using a system frost thermostat.
Fig. 2
3.3
Pump Protection
1. With the selector switch (see Section 2.1) in the ON
position (
minute in every 24 hours to prevent sticking.
). If the system temperature falls below
) the pump will automatically operate for 1
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