Bosch 12/18 User Manual

Burner

motor runs?

Burner

lights 

immediately

motor runs?

23

0V at

solenoid coil

in purge?

Replace

control b

o

x

Replace

pump

23

0V at

motor?

Motor or

pump

seized?

Replace

motor

capacitor

Motor 4

0

Ω

across 

L&

 N

?

L & N

to

control b

o

x?

Control b

o

x

loc

ks out?

Chec

k b

oiler

controls &

supply

Chec

k 

connections/

replace leads

Replace

motor/

pump 

Replace

motor

Replace

control b

o

x

L

o

ckout

within 1

second?

Replace oil

pump

Oil to

pump?

Drive 

coupling

broken?

P

ump

produces

pressure?

Replace

transformer

Electrodes

& leads

OK

?

23

0V at

transformer?

Spark

produced?

L

o

ckout

after purge

before oil

solenoid

opens?

Replace

control b

o

x

Transformer

lead O

K

?

Photo cell

lead O

K

?

Disconnect photo cell,

reset loc

kout, burner

lights then loc

ks out?

Stray light

on photo

cell?

Combustion

head set

correctly?

Combustion

air setting

correct?

Flame off

and

re-lights?

Nozzle

atomising

fuel?

Replace

photo cell

Photo cell

functional?

If B

F

remove

burner

snorkle tube

& retest.

Lights O

K

?

Replace

photo cell

Replace coil

lead

23

0V at

solenoid

coil?

Coil lead

OK

?

Boiler or

flue bloc

ked

Reseal B

F

on

reposition

Replace

control b

o

x

Replace

control b

o

x

S

olenoid

operating?

2.2k

Ω

across 

solenoid

coil?

Pipe to 

nozzle

holder O

K

?

Oil c

h

ec

k

valve O

K

?

(if fitted)

Replace

nozzle

Replace

solenoid coil

Replace

pump

Replace oil

ch

ec

k valve

(if fitted)

Yes

Yes

Yes

No

No

Yes

Yes

No

No

No

No

No

Yes

Yes

No

No

Yes

No

No

Yes

No

Yes

Yes

Yes

No

Yes

Yes

Yes

Yes

No

No

No

Yes

Yes

Yes

Yes

No

No

No

No

No

Yes

Yes

Yes

Yes

Yes

No

No

No

No

Yes

Yes

Yes

Yes

Replace

lead

No

Reset air

setting

No

Reset

combustion

head

No

FAULT FINDING LOGIC FOR 

SATRONIC CONTROL BOX

Note: T

his c

hart assumes all wiring within the control box base is correct

, if in doubt c

hec

k the wiring against the diagram on

the base of the control box before replacing any components

.

All resist

ance measurements are actual measured values and some variation is to be expected

, therefore measured values

should be similar to but not necess

arily identical to the given values

.

T

he operation of the photo cell can be tested by measuring the resist

ance across the photo cell

, it should be a high resist

ance

(greater than 1

0

M

Ω

or open circuit

) in the dark and low resist

ance (

1

5k

Ω

or less

) in light

.

Burners on balanced flue systems can recirculate flue products resulting in the burner cycling

, if this happens c

hec

k the flue

system integrity and the terminal position

. 

These fault finding charts are provided to assist competent and suitably qualified engineers to
locate and rectify faults. Whilst every effort has been taken to ensure the information given is
correct and complete we cannot guarantee that every eventuality has been covered.
Worcester, Bosch Group cannot be held responsible for costs incurred by persons not deemed
to be competent.

Measure all 230V tests between

Neutral (

N

) and the pin

, wire or 

terminal specified

.

FAULT FINDING

INSTALLATION & SERVICING INSTRUCTIONS FOR WORCESTER GREENSTAR HEATSLAVE EXTERNAL 12/18-18/25-25/32
8 716 106 252b (07/06

46

FA

U

LT

 F

IN

D

IN

G

 

& D

IA

G

R

A

M

S