6 720 608 643
42
Problem solving
Cold water temperature sensor
fault.
1. Check connector on wires coming from top of watervalve for a
secure connection. See Fig. 70, page 49.
2. Sensor may trip if water temperature drops below 36°F (2°C).
Protect heater from freezing conditions as any damage due to
freezing conditions is not covered under warranty.
3. Check sensor (ref.
page 46, chapter 10).
Exhaust temperature sensor - the
appliance will close the burner and
lock if it gets over 194°F; (only
applied for condensing unit).
1. Clean and check heat exchanger.
2. Clean and check condensing heat exchanger.
3. Reduce maximum power (
chapter 3.13, page 26).
4. Reduce water temperature.
Backflow temperature sensor over
309°F.
The appliance will close the burner
and lock (non-volatile).
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
chapter 3.12, page 16.
4. Call Bosch Water Heating for further instructions.
Overheat sensor (ECO) open
circuit (resets when cooler
temperatures are detected 220
°F/
104
°C).
1. Disconnect power supply cord and check wire connections on
the overheat sensor (
Fig. 70, page 49) and the two connectors
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
chapter 6.3, page 32.
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.
Display Cause Solution
Table 18
* By installer or service technician only.
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