Bosch C950ES Reference manual

Technical Service Bulletin:

Resetting the Watervalve

Models: 830ES, 940ES-ESO, C950ES, C1050ES, 1210ES-ESC, T9800/T9900 SE(C)

Data subject to change without notice | Printed in the USA | BTC 740002333 A | 05.2018 Bosch Thermotechnology Corp.

A qualiﬁed service technician is recommended to perform the work.

Problem

Tankless water heater that doesn’t activate, and doesn’t show an error code.

Possible Cause

The watervalve may be clogged or needs to be reset.

Overview

Sometimes a tankless water heater doesn’t start up when water is turned on (above

activation rate), and also doesn’t give an error code. This can be due to the impeller

in the watervalve being stuck or clogged, the water valve being closed, or even just

a clogged inlet ﬁlter. Some of the models have an inlet ﬁlter accessible from outside

the machine, which you can inspect for debris ﬁrst. Other models have it directly

in line with the watervalve, in which you will have to disconnect and remove the

watervalve for access.

Procedure

1. Drain the machine down of any water on both the hot and cold sides.

2. Remove the inlet and outlet water clips and remove watervalve from the

machine. After it is removed, disconnect all wiring to the watervalve.

Inspect the screen for any blockage and clean if necessary.

3. Remove the 2 Phillips head screws that hold the watervalve engine to the

watervalve body (Fig. 1).

Figure 1

4. Remove the 2 Phillips head screws that hold the watervalve engine to the

watervalve body (Fig. 1).

5. Separate the 2 the watervalve body and the watervalve engine.

6. On the valve side, locate the brass gear. Rotate the gear counter clockwise

(towards the “0”) until it stops (Fig. 2).

Figure 2

All manuals and user guides at all-guides.com

Data subject to change without notice | Printed in the USA | BTC 740002333 A | 05.2018 Bosch Thermotechnology Corp.

Technical Service Bulletin

2 | Resetting the Watervalve

Bosch Thermotechnology Corp.

65 Grove Street

Watertown, MA 02472

Tel: 1-866-642-3198

Fax: 1-954-776-5529

www.boschheatingandcooling.com

7. On the motor side, slowly rotate the gear clockwise to “0” (Fig. 3). There are

gears inside this motor that cause resistance, do not try to move it fast or

you will damage the gearing.

Figure 3

8. Once that is completed, make sure you can blow through the valve freely

from the bottom where the cross diverter is (Fig. 4). When you forcefully

blow through the valve, you should hear the impeller spinning. If not, use

a small pick or similar device to manually move it. It should move freely

with no resistance. Any resistance could be signs of buildup inside the

valve. Flushing out the valve at this point would be your only way to clear

that obstruction. The impeller is not removable on these valves. If it can’t

spin freely by ﬂushing out the valve or manually rotating it, you may need to

replace the valve.

Figure 4

9. After performing the service, attach the watervalve engine to the watervalve

body with the 2 phillips head screws as shown in Fig. 1.

10. Plug the wiring back in, and reinstall the clips on both the incoming and

outgoing side of the valve.

11. Slowly turn on water supply to check for leaks, before powering up and

returning the tankless unit to service

All manuals and user guides at all-guides.com

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