Bosch Therm C1050ES Technical Service Bulletin

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 control unit front
3 3
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 2
2
1
 Remove control unit from the water heater.
Appliance evaluation for PCB jumper location
3 3
Please evaluate the following prior to installation of the replacement
PCB:
3
2
4
6
8
1
Figure 3
7
5
1