Bosch 12/18 User Manual
Boiler not
operating
with a
heating /
hot water
demand
Burner
motor runs?
L
o
ckout
within 1
second?
Replace
control b
o
x
Replace
motor/pump
Chec
k b
oiler
controls &
supply
Replace
motor
L & N
to
control b
o
x?
Motor or
pump
seized?
Photo cell
functional?
S
olenoid
coil
functional
(100
Ω
)?
Replace
photo cell
Motor gives
50 V
olts on
white wire?
L
o
ckout
after 12 sec
purge?
Replace
control b
ox
Replace
solenoid coil
Replace
motor
Ignition
spark
proved?
Oil to pump?
Drive
coupling
broken?
P
urge
pressure
1-2 bar?
P
ump
produces
pressure?
Replace
pump stem
valve,
pressure
OK
?
Replace
solenoid coil
Pipe to
nozzle
holder O
K
?
Replace
nozzle
Replace oil
pump
Replace
control b
o
x
Eectrodes &
leads O
K
?
Yes
No
NO
Yes
No
Yes
No
Yes
Yes
No
No
Yes
Yes
No
No
Yes
Yes
No
Yes
Motor 4
0
Ω
between blue &
blac
k wires ?
Replace
control b
o
x
Yes
Yes
No
Yes
No
Yes
No
No
No
Yes
No
Nozzle
atomising
fuel?
Combustion
air setting
correct?
Yes
Yes
Combustion
head set
correctly?
S
olenoid operating?
Increase the pump
pressure, pressure O
K
?
S
olenoid
coil
functional
(100
Ω
)?
No
Coil lead
OK
?
Yes
Yes
Replace
control b
o
x
No
Remove
burner
snorkle tube
& retest.
Lights O
K
?
Flame off &
re-lights?
Yes
Photo cell
functional?
No
Yes
Replace
photo cell
No
Boiler or flue
bloc
ked
No
Reseal B
F
Yes
Replace
control b
ox
Yes
Replace
electrodes/
leads
No
Unbloc
k or
replace pipe
No
Reset air
setting
No
Reset
combustion
head
No
FAULT FINDING LOGIC FOR
535 SE/LD RDB CONTROL BOX
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 (3k
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.
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.
F
A
UL
T
F
IND
IN
G
& D
IA
G
R
A
M
S
FAULT FINDING
INSTALLATION & SERVICING INSTRUCTIONS FOR WORCESTER GREENSTAR HEATSLAVE EXTERNAL 12/18-18/25-25/32
8 716 113 389b (09/07)
47