Specifications

Problem solving | 45
6 720 644 887 (2014/11)C 1210 ES/ESC
(Flashing) Water flow signal over specified maximum
value.
Water flow > 10 gallon/min.
(Status message).
1. Disconnect power supply cord and check wire connections on water valve and
the two connectors on the control board, see fig. 83, page 59.
2. Excessive water pressure and flow. Ensure water pressure is less than 150psi
and flow rate is below 10 gallons per minute.
Over-temperature detected by outlet
temperature sensor.
Temperature > 185°F
1. Check wire connection at hot water temperature sensor, see fig. 82, page 58.
2. In areas where water has a high mineral content, periodic descaling may be
necessary. See chapter7.3, page 37 for directions.
3. Check sensor (ref. page 47, chapter 10).
Cold water temperature sensor fault. 1. Check connector on wires coming from top of water valve for a secure
connection. See fig. 76, page 51.
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 48, chapter 11).
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 4.14, page 32).
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 4.3, page 11.
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. 76, page 51) 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 7.3, page 37.
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 40
* By installer or service technician only.