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Bosch C 950 Installation Manual page 51

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Cause
C6
Primary fan rotation too low in
operation.
C7
No rotational speed sensor signal from
primary fan.
(Flashing)
Water flow signal over specified
maximum value.
CA
Water flow > 10 gallon/min.
(Status message).
E1
Over-temperature detected by outlet
temperature sensor.
Temperature > 185°F
E2
Cold water temperature sensor fault.
E3
Exhaust temperature sensor - the
appliance will close the burner and lock
if it gets over 194°F; (only applied for
condensing unit).
E4
Backflow temperature sensor over
309°F.
The appliance will close the burner and
lock (non-volatile).
Table 54
* By installer or service technician only.
Greentherm
Solution
1. Disconnect power supply cord and check wire connection on back side of fan and the
connectors on the control board, see fig. 87, page 65.
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.
1. Disconnect power supply cord and check wire connections on back side of fan and the
two connectors on the control board, see fig. 87, page 65.
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. 87, page 65.
2. Excessive water pressure and flow. Ensure water pressure is less than 150psi and flow
rate is below 10 gallons per minute.
1. Check wire connection at hot water temperature sensor, see fig. 86, page 64.
2. In areas where water has a high mineral content, periodic descaling may be necessary.
See chapter7.3, page 42 for directions.
3. Check sensor (ref. page 54, chapter 10).
1. Check connector on wires coming from top of water valve for a secure connection. See
fig. 80, page 57.
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 55, chapter 11).
1. Clean and check heat exchanger.
2. Clean and check condensing heat exchanger.
3. Reduce maximum power (chapter 4.14, page 36).
4. Reduce water temperature.
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.
Problem solving | 51
6 720 805 440 (2014/11)

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