Fault Finding

Bosch Appliances 28i junior, 24i junior manual Fault Finding

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.

FAULT FINDING

& DIAGRAMS

Blue light	Lockout reset	Fault	Possible solution/check
indication	button	Fault	Possible solution/check
indication	button
Off	Off	No power at control board	Permanent mains supply to boiler.
			Boiler mains switch.
			Fuse F1, 2.5A or Fuse F3, 0.5A
			Transformer (both coils below 100Ω).
			Otherwise replace control board.

On	Off	Boiler not operating during	Live demand at ST10-LR(from external roomstat/timer).
		central heating demand	Facia mounted timer (if fitted).
		(HW ok)	CH knob in winter position.
			Diverter valve.
			Control board.

		Boiler operating	Some older thermostats (containing capacitors) may give a low
		without live demand at	voltage return at ST10-LRwhen the thermostat contacts are open.
		ST10-LR(from external	Check that there is not a permanent live at ST10-LRfrom another
		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.

Slow flash	Flashing (reset required)	Ignition lockout	Gas present and at correct pressure.
(normally off,			Combustion CO2 level.
flashes on)			Flue condition.
flashes on)			Ignition electrodes / harness / connections.
			Ignition electrodes / harness / connections.
			Gas valve (coils 140-190Ω) / low voltage harness connection.
			Otherwise replace control board.

Slow flash	Flashing (reset required)	Flue overheat	Heat exchanger blocked.
(normally on,			Heat exchanger baffles removed and not refitted.
(normally on,
flashes off)		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.

Fast flash	Off	Volatile lockout	Temperature sensor (8000-20,000Ω).
			Low voltage wiring harness / connections to sensor.
			Fan / fan harness / connections to fan.
			Code plug fitted.

Fast flash	Flashing	Internal fault	Replace control board
2 pulses	No light	Not a fault code	Service mode selected to min, press service button to return to normal.

5 pulses	No light	Not a fault code	Service mode selected to max, press service button to return to normal.

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.

FAULT FINDING

INSTALLATION & SERVICING INSTRUCTIONS FOR WORCESTER GREENSTAR 24 i junior/28 i junior 8 716 107 336b (11/05)

28i junior, 24i junior specifications

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