
FA
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INSTALLATION & SERVICING INSTRUCTIONS
48
FAULT FINDING
6-720-611-730b (12.05)
NOTE ; This fault finding information is for guidance
only. Worcester Bosch cannot be held responsible
for costs incurred by persons not deemed to be
competent.
The electronic control system for this boiler
incorporates a two-digit display. This is used to
show normal operating information (as described
in other sections), but during a fault, also provides
fault-code information to help provide fault
diagnostics. This covers most normal fault situations.
FAULT FINDING
Check, repair/replace as necessary:
Tank sensor (8000 - 20000 ohms at room temperature).
Wiring and connections to sensor.
Check link 8 to 9 in connector ST3.
DHW sensor (8000 - 20000 ohms at room temperature).
Wiring and connections to sensor.
Night set back module TR212E and/or Roomstat TR2.
Wiring and connections between modules.
Code plug version, condition and fitting.
If OK replace control board.
Fan harness and connections.
Fan.
Otherwise replace control board.
Safety overheat thermostat for underfloor heating system
(if fitted).
Otherwise fit link.
Mains supply to condensate pump.
Condensate Pump unit.
Continuity of all cables to pump unit.
Tank sensor is correctly fixed to tank
Wiring and connections to sensor.
CH flow sensor (8000 - 20000 ohms at room
temperature).
Wiring and connections to sensor.
All air vented.
Water pressure above minimum.
Leaks or blockage.
Condition and attachment of CH flow sensor.
Pump and associated wiring/connections.
Connections and wiring to overheat thermostat devices.
Otherwise replace control board.
Gas present and at correct pressure.
Combustion C02 level.
Condition of flue.
Ignition electrodes.
Ignition harness and connections.
Flame sense harness.
Flame sense cables and connections.
Gas valve.
Otherwise replace control board.
Display
Code:
A5
A6
A7
A8
b1
C1
d3
d5
d6
E2
E9
EA
Fault description:
Tank sensor fault
Link fault
DHW sensor fault
Module fail
Code plug not detected
Fan speed too low
Terminals 8-9 not shorted
at connector ST7
Condensate pump failed
Tank overheat
CH flow sensor fault
Safety overheat device
tripped
Flame not detected