Fault Finding & Diagnosis; Fault Finding - Bosch Worcester GREENSTAR 12i System Instruction Manual

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 blue central indicator. This normally confirms the permanent mains supply but, by
flashing at different rates during a fault, provides a guide to the cause as listed.
This fault finding system assumes that the appliance has been operating normally until the time of failure (i.e. not a first installation error).
PRELIMINARY CHECKS : Preliminary electrical system checks are the first electrical checks to be carried out during a fault-finding
procedure. On completion of the Service/Fault-Finding task which has required the breaking and remaking of electrical connections, check
(a) EARTH CONTINUITY, (b) SHORT CIRCUIT CHECK, (c) POLARITY and (d) RESISTANCE TO EARTH.
Lockout reset
Blue light
indication button
Off Off
On
Off
Flashing (reset required)
Slow flash
(normally off,
flashes on)
Flashing (reset required)
Slow flash
(normally on,
flashes off)
Fast flash
Off
Fast flash Flashing
2 pulses No light
5 pulses
No light
INSTALLATION & SERVICING INSTRUCTIONS FOR WORCESTER BOSCH GREENSTAR 12i System/24i System
8 716 107 375a (02/05)
Fault Possible solution/check
Permanent mains supply to boiler.
No power at control board
Boiler mains switch.
Fuse 4, 2.5A or Fuse 6, 0.5A
Transformer (both coils below 100Ω).
Otherwise replace control board.
Boiler not operating during External diverter valve.
central heating demand External timer or room stat
OR
(HW ok)
If optional diverter valve is fitted:
Temperature control in frost protection position.
Live demand at ST10-L
Facia mounted timer (if fitted).
Diverter valve.
Control board.
Boiler not operating during External diverter valve.
External timer or cylinder stat
hot water demand (CH ok).
OR
If optional diverter valve is fitted:
Short circuit across ST8 from cylinder stat/timer.
Facia mounted timer (if fitted).
Diverter valve.
Control board.
Boiler not operating during Temperature control in frost protection position.
Live demand at ST10-L
any demand.
Control board.
OR
If optional diverter valve is fitted:
Timer.
Control board.
Ignition lockout Gas present and at correct pressure.
Combustion CO 2 level.
Flue condition.
Ignition electrodes / harness / connections.
Gas valve (coils 140-190Ω) / low voltage harness connection.
Otherwise replace control board.
Flue overheat Heat exchanger blocked.
Heat exchanger baffles removed and not refitted.
Heat exchanger overheat Water pressure.
All air vented.
Pump / harness / connections.
Water leaks / blockages.
Safety thermostats / low voltage wiring harness / connections.
Otherwise replace control board.
Blockage in flue system.
Flue blockage
Volatile lockout
Temperature sensor (8000-20,000Ω).
Low voltage wiring harness / connections to sensor.
Fan / fan harness / connections to fan.
Code plug fitted.
Replace control board
Internal fault
Service mode selected to min, press service button to return to normal.
Not a fault code
Not a fault code
Service mode selected to max, press service button to return to normal.

FAULT FINDING

(external CH demand).
R
(from external system).
R
FAULT FINDING
55