Fault Finding & Diagnosis; Fault Finding - Worcester GREENSTAR 24i junior Instruction Manual

NOTE : This fault finding information is for guidance only. Worcester 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.
Blue light Lockout reset
indication button
Off
Off
On
Off
Slow flash
Flashing (reset required)
(normally off,
flashes on)
Slow flash Flashing (reset required)
(normally on,
flashes off)
Fast flash
Off
Fast flash
Flashing
2 pulses
No light
5 pulses No light
Flow Sensor Test
:Replace control board if: 5V is not across the red and black cables.
:1.5V-3.5V is across the yellow and black cables (with water flowing).
Otherwise replace flow sensor.
55

FAULT FINDING

Fault Possible solution/check
Permanent mains supply to boiler.
No power at control board
Boiler mains switch.
Fuse F1, 2.5A or Fuse F3, 0.5A
Transformer (both coils below 100Ω).
Otherwise replace control board.
Live demand at ST10-L
Boiler not operating during
Facia mounted timer (if fitted).
central heating demand
CH knob in winter position.
(HW ok)
Diverter valve.
Control board.
Boiler operating
Some older thermostats (containing capacitors) may give a low
without live demand at
voltage return at ST10-L
ST10-L (from external
Check that there is not a permanent live at ST10-L
R
roomstat timer).
source.
Boiler not operating during
See Flow Sensor Test below.
hot water demand (CH ok).
or
Diverter valve.
Control board.
Boiler not operating during
Fan.
any demand.
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.
Flue blockage
Blockage in flue system.
Volatile lockout
Temperature sensor (8000-20,000Ω).
Low voltage wiring harness / connections to sensor.
Fan / fan harness / connections to fan.
Code plug fitted.
Internal fault Replace control board
Not a fault code
Service mode selected to min, press service button to return to normal.
Not a fault code
Service mode selected to max, press service button to return to normal.
INSTALLATION & SERVICING INSTRUCTIONS FOR WORCESTER GREENSTAR 24 i junior/28 i junior
FAULT FINDING
(from external roomstat/timer).
R
when the thermostat contacts are open.
R
from another
R
8 716 107 336b (11/05)