Bosch 425HN Service Bulletin

CT-27 | 1600H, 425HN
Service bulletin
Replacing control box
Tools needed:
Phillips head screwdriver

Needle-nosed pliers

Removing ignition unit
1. Close installer supplied cold water shut off valve to water heater.
2. Remove front cover of heater. (See instructions in the installa-
tion manual)
3. Remove single ignition wire connection (to spark electrode)
from upper left corner of ignition unit. Unclip wire from bracket
on top of ignition unit (425HN models only). (See Fig. 1)
4. Remove multiple wire connector from lower right corner of
ignition unit by gently pulling outwards with needle-nosed pliers.
(See Fig. 1)
5. Remove screw with ground wire connection from upper right
corner of ignition unit Metal bracket and ignition unit will drop
out of heater.
6. Remove ignition unit from metal bracket.
Control box (425HN model shown)
Installing ignition unit
1. Insert tab on lower left of ignition unit into slot in lower left of
metal bracket.
2. Mount ignition unit with bracket to heater by inserting screw
into upper right hand corner.
Note: Feed screw through ground wire eyelet with washer before
threading through ignition unit to heater. (See Fig. 1)
3. Press multiple wire connector into lower right of ignition unit.
4. Push ignition wire on to single terminal in top left corner of
ignition unit. Clip wire into bracket on top of ignition unit
(425HN models only).
5. If a replacement hydro generator (black and red lead wires) was
sent as a temporary solution for ignition failure, please reinstall
original hydro generator, part# 8707406071 (blue and brown
lead wires).
6. Install front cover, open cold water supply and return heater to
service.
Figure 1