44 | Problem solving
C 1210 ES/ESC6 720 644 887 (2013/02)
Primary fan rotation too low in operation. 1. Disconnect power supply cord and check wire connection on back side of fan
and the connectors on the control board, see fig. 83, page 59.
2. Check supply voltage. It must be 120VAC and properly grounded.
3. Check venting specifications are met. Long vent lengths, venting with more
than three elbows, blocked vent or combination venting may cause this failure.
4. Ensure intake and exhaust terminations maintain the required clearances
stated in the manual. Cross contamination between intake and exhaust may
cause the fan to alter its rotational speed.
5. Check gas pressure. Low gas pressure may cause the fan to change its speed
to meet desired temperature.
6. Possible defective control unit call Bosch Water Heating for further
instructions.
No rotational speed sensor signal from
primary fan.
1. Disconnect power supply cord and check wire connections on back side of fan
and the two connectors on the control board, see fig. 83, page 59.
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.
(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 36 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 31).
4. Reduce water temperature.
Display Cause Solution
Table 39
* By installer or service technician only.
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