FAULT FINDING AND DIAGNOSIS
6 720 804 532 (2012/09)
50
7
FAULT FINDING AND DIAGNOSIS
7.1
FAULT FINDING
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
indication
Lockout reset
button
Fault
Possible solution/check
Off
Off
No power at control
board
Permanent mains supply to boiler.
Fuse F1 - 2.5A.
Otherwise replace control board.
On
Off
Boiler not operating
during central heating
demand (HW ok)
Live demand at ST10-L
R
(from external room thermostat/timer)
Fascia mounted timer (if fitted)
CH knob in winter position
Diverter valve
Control board
Boiler operating without
live demand at ST10-L
R
(from external room
thermostat timer)
Some older thermostats (containing capacitors) may give a low voltage return at ST10-L
R
when the thermostat contacts are open.
Check that there is no permanent live at ST10-L
R
from another source.
Boiler not operating
during hot water demand
(CH ok)
Ensure cold inlet DHW outlet are correctly piped i.e. are not crossed piped.
If the optional Integral Diverter Valve kit has been fitted, check diverter valve and motor and
control board.
Boiler not operating
during any demand.
Fan
Control board
Slow flash
(mostly off,
flashes on)
Flashing (reset
required)
Ignition lockout
▶ Gas present and at correct pressure?
▶ Gas valve
– Check that there is 35V d.c. to each solenoid
– Check the resistance of each solenoid: Top solenoid = 380
Ω
±
10% (342 - 418
Ω
)
Bottom solenoid = 190
Ω
±
10% (171 - 209
Ω
)
▶ Combustion CO
2
level.
▶ Flue condition - Blocked flue?
▶ Blocked condensate pipe or frozen condensate.
▶ Gas valve adjustment.
▶ Ignition electrodes/harness/connections - Check for condition and resistance of leads
(approximately 2100
Ω
).
▶ Otherwise replace control board
Slow flash
(mostly on,
flashes off)
Flashing (reset
required)
Flue overheat
▶ Heat exchanger baffles removed and not refitted.
Heat exchanger overheat ▶ Heat exchanger blocked
▶ Water pressure
▶ All air vented
▶ Pump/harness/connections.
▶ Water leaks/blockage
▶ Safety thermostats/low voltage wiring harness/connections
▶ Otherwise replace control board
Fast flash
Off
Volatile lockout -
Fan does not run
▶ Temperature sensors - Check condition and continuity of leads and resistance of sensors
(approximately 2100
Ω
)
▶ Fan - 230V a.c. across the live (purple) and neutral (brown)
▶ Fan lead - Check continuity
▶ Code plug - Is the code plug missing or not inserted properly
Fast flash
Flashing
Internal fault
Replace control board
2 pulses
No light
Not a fault code
Service mode selected to minimum, press service button to return to normal
5 pulses
No light
Not a fault code
Service mode selected to maximum, press service button to return to normal