Bosch C1050ES Reference manual

Technical Service Bulletin:
Replacing The Control Unit
Models: C1050ES, C950ES, 940ES, 940ESO, 830ES
Introduction
Tools needed:
Phillips head screw driver
Small flat head screw driver
Needle-nosed pliers
Note: Avoid touching printed circuit board (PCB) as static discharge
may damage circuitry.
Preparation
Push power button to "OFF" and unplug power cord.
Loosen two Phillips head screws on bottom rear of front cover.
Pull cover bottom outwards then lift cover upwards to remove.
Removing control unit
Remove three Phillips screws on front of control unit. (Fig. 2,
pos. 1)
Turn control unit to expose the rear. (Fig. 2, pos. 2).
Locate and remove 6 Phillips head screws on back of control
unit (Fig. 2, pos. 3).
control unit front
3
3
co
n
t
r
o
l
u
ni
t
f
r
o
n
t
3
3
Figure 2
Remove rear cover from control unit to expose circuit board
electrical connections. Slide wire restraints out of control unit.
(Fig. 3, pos. 1).
Remove two large electrical strip connectors by pulling them
away from board. (Fig. 3, pos. 2).
Remove medium sized electrical strip connector by pulling it
outwards. (Fig. 3, pos. 3).
Remove small electrical strip connector by pulling it outwards.
(Fig. 3, pos. 4).
Remove two large ignition wires by pulling them outwards. (Fig.
3, pos. 5).
Remove yellow/green striped ground wire spade connection by
depressing tab on connector and pulling it gently off the board.
(Fig. 3, pos. 6).
Loosen two small flat head screws on terminal block for power
cord. Pull black and white wires free from terminal block and
control unit. (Fig. 3, pos. 7).
Loosen Phillips head screw and remove green ground wire con-
nection for power cord. (Fig. 3, pos. 8).
Figure 3
1
1 1
2
23
45
6
7
8
Remove control unit from the water heater.
Appliance evaluation for PCB jumper location
Please evaluate the following prior to installation of the replacement
PCB:

2
|Replacing The Control Unit Technical Service Bulletin
Data subject to change without notice | Printed in the USA | BTC 740002317 C | 06.2012 Bosch Thermotechnology Corp.
Locate rating plate sticker on right side of heater cover.
Determine model number (Fig.1, pos.A) and gas type (Fig.1,
pos.B).
Figure 1
Locate hot water outlet pipe (Fig.2, pos.A). Determine the type
of outlet temperature sensor installed on the hot water outlet
pipe (Fig.3).
Figure 2
Figure 3
Surface mount outlet
temperature sensor
Immersed outlet
temperature sensor
PCB jumper installation
In order for the appliance to work correctly, the proper jumpers
must be installed on the PCB board. (Fig.4)
Backside of control unit
B
ackside o
f
control uni
t
Figure 4
Based on your model, gas type and type of outlet temperature
sensor, jumpers should be installed on the PCB in the following
arrangement:
C 950 ES or 830 ES with surface mount outlet temperature
sensor
Natural
Gas
N
atura
l
Gas
Figure 5
Liquid
Propane
C 950 ES or 830 ES with immersed outlet temperature sensor
Figure 6
NO
JUMPER
NEEDED
Natural
Gas
Liquid
Propane

3
|Replacing The Control Unit Technical Service Bulletin
Data subject to change without notice | Printed in the USA | BTC 740002317 C | 06.2012 Bosch Thermotechnology Corp.
Bosch Thermotechnology Corp.
50 Wentworth Avenue
Londonderry, NH 03053
Tel: [phone]
Fax: [phone]
www.bosch-climate.us
C 1050 ES or 940 ES/ESO with surface mount outlet
temperature sensor
Figure 7
Natural
Gas
Liquid
Propane
C 1050 ES or 940 ES/ESO with immersed outlet temperature
sensor
Figure 8
Natural
Gas
Liquid
Propane
Replacing control unit
Once the appropriate jumpers have been determined, remove
rear cover of replacement control unit.
Install jumpers in the proper location on PCB.
Connect green ground wire from power cord to replacement
control board with Phillips head screw. (Fig. 3, pos. 8).
Reconnect black and white power cord wires to terminal
block on replacement control unit; Black -L (Load), White - N
(Neutral). Secure to terminal block by tightening flat head
screws. (Fig. 3, pos. 7).5. Reconnect yellow/green striped
ground wire to spade connection on replacement control
board. (Fig. 3, pos. 6).
Reattach large ignition wires to replacement control board (no
polarity). (Fig. 3, pos. 5).
Reconnect small electrical strip connector to replacement
control board. (Fig. 3, pos. 4).
Reconnect medium sized electrical strip connector to
replacement control board. (Fig. 3, pos. 3).
Reconnect two large electrical strip connectors to replacement
control board. (Fig. 3, pos. 2).
Reseat rubber wire restraints in control unit. (Fig. 3, pos. 1).
Replace rear cover on unit using 6 Phillips screws. (Fig. 2, pos.
3).
Place control unit back into water heater and secure with 3
Phillips head screws. (Fig. 2, pos. 1).
Plug water heater power cord back into electrical outlet and
push On/Off button on water heater to "ON".