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15.0 FAULT FINDING
42
Publication No. 5111811
Domestic Hot Water - Follow operational sequence
Turn selector to
neon illuminated
Primary flow switch
operated
Fan runs at max speed
Pump runs
Turn thermostat to
max. Open DHW tap fully.
DHW flow switch operated
Primary water is diverted
from CH system to DHW
heat exchanger and flow
microswitch operated
Continuity across DHW
flow microswitch
terminals and PCB - M1
connector terminals 13 &
14 (terminals 12-14 open)
Air pressure switch
proved
neon illuminated
Burner on neon
illuminated
Spark at ignition
electrodes for up to 10
seconds
Go to section ‘A’
Go to section ‘B’
Go to section ‘C’
Go to section ‘J’, ‘L’ & ‘D’
Replace PCB
Turn the selector to the
reset position. If the light
does not extinguish go to
section H & K
Go to section ‘F’
Go to section ‘I’
DHW flow valve
senses no flow.
Primary water diverted to
CH system. DHW flow
switch released off
Close DHW tap
Burner goes out
Diverter valve spindle
assembly faulty
Pump stops
Operation sequence
correct
Turn the selector switch
to the ‘Reset’ position
and hold for at least 2
seconds. If regular
resetting is required, or
appliance still does not
operate investigation is
necessary
Go to section ‘E’
Burner extinguishes
after 10 seconds
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
Fan stops
NO
YES
YES
YES
NO
NO
DHW flow rate more than
2.5l/min.
Is mains water
filter and differential
assembly clean?
DHW flow valve
diaphragm damaged
DHW flow valve rod
obstructed
Replace DHW flow
microswitch
Replace PCB
Replace diaphragm
NO
NO
NO
YES
NO
NO
NO
NO
NO
NO
NO
NO
Reduce the DHW flow
rate. If burner does not
modulate clean
temperature sensor and
DHW heat exchanger. If
modulation does not
occur go to section ‘G’
Burner output modulates
to maintain temperature
set at thermostat
NO