Off
On
Slow flash
(normally off,
flashes on)
Slow flash
(normally on,
flashes off)
Fast flash
Fast flash
2 pulses
5 pulses
Off
Off
Flashing (reset required)
Flashing (reset required)
Off
Flashing
No light
No light
Permanent mains supply to boiler.
Boiler mains switch.
Fuse 4, 2.5A or Fuse 6, 0.5A
Transformer (both coils below 100
Ω
).
Otherwise replace control board.
External diverter valve.
External timer or room stat
OR
If optional diverter valve is fitted:
Temperature control in frost protection position.
Live demand at ST10-L
R
(external CH demand).
Facia mounted timer (if fitted).
Diverter valve.
Control board.
External diverter valve.
External timer or cylinder stat
OR
If optional diverter valve is fitted:
Short circuit across ST8 from cylinder stat/timer.
Facia mounted timer (if fitted).
Diverter valve.
Control board.
Temperature control in frost protection position.
Live demand at ST10-L
R
(from external system).
Control board.
OR
If optional diverter valve is fitted:
Timer.
Control board.
Gas present and at correct pressure.
Combustion CO2 level.
Flue condition.
Ignition electrodes / harness / connections.
Gas valve (coils 140-190
Ω
) / low voltage harness connection.
Otherwise replace control board.
Heat exchanger blocked.
Heat exchanger baffles removed and not refitted.
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.
Temperature sensor (8000-20,000
Ω
).
Low voltage wiring harness / connections to sensor.
Fan / fan harness / connections to fan.
Code plug fitted.
Replace control board
Service mode selected to min, press service button to return to normal.
Service mode selected to max, press service button to return to normal.
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.
FAULT FINDING
FAULT FINDING
INSTALLATION & SERVICING INSTRUCTIONS FOR WORCESTER BOSCH GREENSTAR 12i System/24i System
8 716 107 375a (02/05)
55
F
A
UL
T
F
IND
IN
G
& D
IA
G
R
A
M
S
Blue light
indication
Lockout reset
button
Possible solution/check
Fault
No power at control board
Boiler not operating during
central heating demand
(HW ok)
Boiler not operating during
hot water demand (CH ok).
Boiler not operating during
any demand.
Ignition lockout
Flue overheat
Heat exchanger overheat
Flue blockage
Volatile lockout
Internal fault
Not a fault code
Not a fault code
