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14.0 Fault Finding
Domestic Hot Water - Follow operational sequence
Primary flow switch operated
Fan runs at max speed.
Pump runs
Turn preheat control to on.
Preheating function starts after
25 seconds.
neon flashing.
Primary water is diverted from
preheating circuit to DHW
heat exchanger.
neon illuminated
Air pressure switch proved.
neon flashing
Spark at ignition electrode for
up to 10 seconds.
neon flashing
Go to section ‘B’
neon flashing
Go to section ‘C’
neons flashing
Go to section ‘D’
neon flashing
Go to section ‘I’ & ‘N’.
Turn the selector to reset.
If regular resetting is required
or appliance still does not
operate investigation is
necessary.
neon flashing
Go to section ‘E’
YES
YES
YES
NO
Turn On/Off/Reset selector to
position.
neon illuminated.
Primary water diverted to
DHW preheating circuit.
Open DHW tap fully. DHW
flow switch operated.
Burner lights.
Burner output modulates to
maintain temperature set at
preheat control.
Burner goes out.
Burner extinguishes after 10
seconds.
NO
Close DHW tap.
DHW flow valve senses no
flow. DHW flow switch
released off.
Preheating function restarts.
neon flashing
Go to section ‘A’.
Go to section ‘M’.
External controls and where
fitted, integral timer calling for
heat.
Go to section ‘L’.
Ensure controls are set to
demand and verify the contacts
are closed.
DHW flow rate more than 2.5
l/min.
Is mains water filter and
differential assembly clean?
DHW flow valve diaphragm
damaged.
Replace diaphragm.
DHW flow valve rod
obstructed.
Continuity across DHW flow
microswitch terminals and PCB
- A5 connector terminals 5 & 6
Replace DHW flow
microswitch.
Replace main PCB
Go to section ‘J’ or ‘O’.
Turn selector to the reset
position. If the neon does not
extinguish go to sections H and
K.
Change main PCB.
Go to section ‘F’.
Reduce the DHW flow rate. If
burner does not modulate
clean DHW temperature
sensor and DHW heat
exchanger. If modulation does
not occur go to section ‘G’.
External controls and where
fitted, integral timer calling for
heat.
Fan stops.
Pump continues to
run for 30 seconds.
Operation sequence
correct
Ensure controls are set to
demand and verify the controls
are closed.
Go to section ‘L’.
YES
NO
NO
YES
NO
NO
YES
YES YES
YES
YES
NO
NO
YES
YES
NO
NO
YES
YES
NO
YES
NO
NO
YES
NO
NO
YES
YES
NO
NO
YES
YES
YES
NO
YES
YES
YES
YES
YES
neon flashing
NO
YES
NO