FAULT FINDING & DIAGNOSIS
6 720 806 548 (2013/02) 41
7 FAULT FINDING & DIAGNOSIS
7.1 FAULT FINDING
The electronic control system for this boiler incorporates a blue central
indicator. This normally confirms the permanent mains supply but, by
flashing 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
(d) RESISTANCE TO EARTH
More detailed fault finding procedures are described in the Service booklet for the Engineer number 6 720 612 361.
7.2 PROTECTION FUNCTION (EXTERNAL PUMP)
This fault finding information is for guidance only.
Worcester Bosch cannot be held responsible for costs
incurred by persons not deemed to be competent.
Display
code Description Remedy
b1 Code plug not detected. Insert code plug correctly, test and replace if necessary.
C6 Fan speed too low. Check fan lead and connector, and fan; replace as necessary.
E2 CH flow NTC sensor defective. Check CH flow NTC sensor and connecting lead.
E9 Safety temperature limiter in CH flow has tripped. Check system pressure, check safety temp. limiters, check pump operation,
check fuse on pcb, bleed appliance.
EA Flame not detected. Is gas cock turned on? Check gas supply pressure, power supply, igniter
electrode and lead, ionisation sensing electrode and lead, flue duct and CO2
level.
F0 Internal error. Check electrical connector contacts, programmer inter-face module ignition
leads are not loose; replace pcb if necessary.
F7 Flame detected even though appliance switched off. Check electrode assembly, dry pcb. Flue clear?
FA Flame detected after gas shut off. Check gas valve and wiring to gas valve. Clean condensation trap and check
electrode assembly. Flue clear?
Fd Reset button pressed by mistake Press reset button again
Table 20
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