Bosch Worcester 15SBi Installation And Servicing Instructions page 32

BOILER DEMAND TEST
Set the system to create a boiler demand. Turn facia control knob to maximum.
Does the boiler pump
run?
(removal of pump
venter plug may help
identify rotation of
pump)
Yes
Does the Fan
run?
Yes
Is the facia
No No
indicator
still on?
Yes
Does the fan run and
normal ignition
take place?
Yes
Is there 230V AC
across both pins of
connection X5?
Yes
Replace the Pump.
(Section 15.4.12)
No
No
Press the facia
reset button.
Does the fan run
after approx
20 seconds?
Yes
Control was in a lock
out condition.
There are two main
causes for this:
gas/ignition problem
or limit thermostat
tripping.
Continue fault finding
sequence:
Refer to
above section
Drop down the facia
and expose the three
No
PCB rear connectors.
Is there 230V at pins
3 & 4 of connector
X11?
(centre connector)
Yes
No
Replace control board.
(Section 15.4.9)
No
Is there 230V AC
across both pins
of connector
X4?
32
The system is not
No
creating a boiler
demand. Refer to
SYSTEM TEST
No
Switch off mains
supply.
Remove Molex
connector at X6 and
measure the
resistance across the
red wires. Is the
resistance below
50k ohms?
Yes
No
Measure the continuity
across the green wires.
Is it open circuit?
Yes
Remove Molex connector at X3
and measure the resistance
across the two wires that run to
the gas valve.
Is the resistance between
3000 and 5000 ohms?
Yes
Replace control board.
(Section 15.4.9)
Check or replace
temperature
sensor or sensor
harness.
Replace air
pressure switch.
No
Replace gas
valve or cable
to gas valve.