Bosch 940 ESO Installation Manual page 40

Problem solving
Display Cause
(Flashing) Outlet temperature sensor not
sensing
temperature.
(Status message, not an error).
Primary fan rotation too low on
operation.
No rotational speed sensor signal
from primary fan.
(Flashing) Water flow signal over specified
maximum value.
Water flow > 10 gallon/min.
(Status message, not an error).
Over-temperature
outlet temperature sensor on hot
water pipe.
Temperature > 185°F
Table 12
* By installer or service technician only.
40
Solution
1. Check that the sensor is firmly attached to the hot water pipe
expected output (see Fig.
2. Ensure that outlet temperature sensor is not placed on any
bends in the hot water pipe or misreading may occur.
3. Check gas pressure. Low gas pressure may prevent the heater
from reaching desired output temperature.
4. Check supply voltage. It must be 120VAC and properly
grounded.
5. Possible defective control unit call Bosch Water Heating for
further instructions.
1. Disconnect power supply cord and check wire connection on
back side of primary fan and the connectors on the control board
(see Fig.
2. Check supply voltage. It must be 120VAC and properly
grounded.
3. Check vent openings. A blockage may cause this failure.
4. Check gas pressure. Low gas pressure may cause the fan to
change its speed to meet desired temperature.
5. Possible defective control unit call Bosch Water Heating for
further instructions.
1. Disconnect power supply cord and check wire connections on
back side of primary fan and the two connectors on the control
board (see Fig.
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.
2. Excessive water pressure and flow. Ensure water pressure is
less than 150psi and flow rate is below 10 gallons per minute.
detected by 1. Check that the sensor is firmly attached to the vertical section of
the hot water pipe (see Fig.
2. Check red wire connections at outlet temperature sensor.
Clean terminals with an eraser. If badly corroded, replace sensor
and wire harness.
3. In areas where water has a high mineral content, periodic
descaling may be necessary. See chapter
directions.
4. Check sensor (ref.
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chapter 13
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