Bosch GWH C 800 ES Installation Instructions Manual page 42

Problem solving
Display Cause
Cold water temperature sensor
fault.
Exhaust temperature sensor - the
appliance will close the burner and
lock if it gets over 194°F; (only
applied for condensing unit).
Backflow temperature sensor over
309°F.
The appliance will close the burner
and lock (non-volatile).
Overheat sensor (ECO) open
circuit
temperatures are detected 220
°C
104
Table 18
* By installer or service technician only.
42
(resets when cooler
°
F/
).
Solution
1. Check connector on wires coming from top of watervalve for a
Fig. 70
secure connection. See
2. Sensor may trip if water temperature drops below 36°F (2
Protect heater from freezing conditions as any damage due to
freezing conditions is not covered under warranty.
page 46, chapter 10).
3. Check sensor (ref.
1. Clean and check heat exchanger.
2. Clean and check condensing heat exchanger.
3. Reduce maximum power (
4. Reduce water temperature.
1. Check inlet/outlet vent pipes.
2. Check if secondary fan connections are disconnected.
3. Check if venting specifications are met. Long vent lengths,
venting with more than three elbows, blocked vent or combination
venting may cause this failure. See
4. Call Bosch Water Heating for further instructions.
1. Disconnect power supply cord and check wire connections on
Fig. 70
the overheat sensor (
on the control board.
2. Check white wire connections at the overheat sensor. Clean
terminals with an eraser. If badly corroded, replace sensor and
wire harness.
3. Check that venting specifications are met. Long vent lengths,
venting with more than three elbows, blocked vent or combination
venting may cause this failure.
4. In areas where water has a high mineral content, periodic
descaling may necessary, see
5. Unplug power supply cord to the water heater. Open a hot
water tap for several minutes to allow cold water to pass through
heat exchanger. Close hot water tap and disconnect lead wires to
overheat sensor. Using a multimeter, check continuity through
overheat sensor contacts. Replace sensor if open.
page 49
, .
chapter 3.13 page 26
, ).
chapter 3.12 page 16
,
page 49
, ) and the two connectors
chapter 6.3 page 32
, .
6 720 608 643
°
C).
.