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FAIL POINT C
Is the boiler in a very cold
environment
i.e is the primary water
temperature below 5°C?
Boiler is running in
'Autofroststat' mode.
Yes
Demand light has
failed. Replace control
board if it is
considered a problem.
No
FAIL POINT D
Is the system fully
water pressurised
and is all air vented?
The system should have a
bypass fitted as described in
Section 7. SYSTEM and Figs.
5, 6 & 7. Is bypass fitted and
correctly adjusted?
Yes
Remove connector at X5.
With boiler cool is there a
short circuit between the
orange & black cables?
Reset the lockout and create
a boiler demand.
With the boiler cool does
the pump run?
Yes
Switch off mains supply.
Remove boiler cover
and inspect the
temperature sensor.
Is it correctly fitted to the
manifold with heat
conductive paste on its
surface?
Yes
Gain access to control board
and inspect the slide switch
at the front of the board.
In normal domestic
installation this switch
should be in the left
'normal' position.
Yes
Yes
Yes
Replace control board.
Rectify fault/leak.
No
Add or adjust system
bypass.
No
No
Replace pump or
check cables to it.
No
Refit sensor to
manifold or add heat
conductive paste.
No
Use a suitable
implement to push
switch to the 'normal'
left position. The
'heatstore' right position
is for commercial
applications only.
No
Replace overheat
thermostat or check
wiring to it.
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