Bosch 15SBI Service Manual download pdf (Page 35)

Set the system to

end the boiler

demand.

Does the burner

shut down?

The system is not creating

a demand signal at the

control board

Is the system fully

prewired at a junction box

remote from the boiler (see

Worcester system wiring

guide. Page 4)

Boiler is used as a wiring

centre for Y plan or S plan

system. Firstly check the

“IMPORTANT NOTES” on

the appropriate page of

the Worcester wiring

guide. If problem is not

solved then continue..

To simplify the demand

situation set the system

for DHW ONLY (CH timed

off, HW timed on, cylinder

cold). Is there 230V now at

X11 pins 3 & 4?

Now also create a CH

demand (roomstat to max

and CH timed on). Is there

230V at X11 pins 1 & 4.

Is there 230V

across pin 1 of

connector X10

and pin 4 of

connector X11?

NOTE

X10, X11 and X12 are the three connectors on the rear of

the boiler control board

Is there 230V

across X12 pin 3

and X11 pin 4?

Is there 230V

across X10 pin 3

and X11 pin 4?

Replace cylinder

thermostat

Check or replace

programmer/

timeclock

Check or replace

room thermostat

For Y plan

system: Replace

control board.

For S plan

system: Replace

DHW zone valve

For Y plan system: Replace

mid-position valve. For S

plan system: Replace CH

zone valve.

Complete systems outside

the boiler are not the

responsibility of Worcester

Heat Systems. But as a

fault finding guide: Check

the “IMPORTANT NOTES”

on Page 4 of the wiring

guide booklet and use any

proprietary information

from the junction box

supplier

Drop down the facia

and expose the three

PCB rear

connections.

Measure AC voltage

at pins 3 & 4 of

connection X11.

This should be OV.

System is still creating a demand.

Check appropriate “IMPORTANT NOTES” section

of the wiring guide booklet. If this does not

highlight the probable cause of problem, then

the fault is very likely to be: mid-position valve if

Y plan DHW, or CH zone valve is S plan.

Does the pump

continue to run for

approx 3 minutes?

(failure to do so may

cause overheat

problems).

Yes

Replace control board.

(Section 15.4.9)

Yes

END OF TEST

SYSTEM TEST

This test assumes the system is set to create a boiler demand, but mains voltage is not present at the connector X11 pins 3 & 4

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Bosch 15SBI Service Manual Page 35

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