Bosch 940 ES Installation And Operating Instructions Manual page 61

Display Cause
No rotational speed sensor signal
from primary fan.
(Flashing) Water flow signal over specified
maximum value.
Water flow > 10 gallon/min.
(Status message).
Over-temperature detected by
outlet temperature sensor.
Temperature > 185°F
Cold water temperature sensor
fault.
Backflow temperature sensor
over 309°F.
The appliance will close the
burner and lock (non-volatile).
Overheat sensor (ECO) open
circuit (resets when cooler
temperatures are detected
220°F/104 °C).
940 ES – 6 720 644 930 (2019/09)
Solution
1. Disconnect power supply cord and check wire connections on back side of fan
and the two connectors on the control board, see fig. 74, page 74.
2. Check supply voltage. It must be 120VAC and properly grounded.
3. Possible defective component in fan or defective control unit call Bosch Water
Heating for further instructions.
1. Disconnect power supply cord and check wire connections on water valve and
the two connectors on the control board, see fig. 74, page 74.
2. Excessive water pressure and flow. Ensure water pressure is less than 150psi
and flow rate is below 10 gallons per minute.
1. In areas where water has a high mineral content, periodic descaling may be
necessary. See chapter 7.3, page 52 for directions.
2. Check sensor (ref. page 63, chapter 10).
1. Check connector on wires coming from top of water valve for a secure
connection. See fig. 67, page 67.
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 64, chapter 11).
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 15.
4. Call Bosch Water Heating for further instructions.
1. Disconnect power supply cord and check wire connections on the overheat
sensor (fig. 67, page 67) 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 52.
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.
Problem solving
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