6 720 608 643
Problem solving
41
Primary fan rotation too low on
startup.
1. Disconnect power supply cord and check wire connections on
back side of fan and the two connectors on the control board, Fig.
77
, page 57.
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. 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.
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.
77
, page 57.
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. 77, page 57.
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.
77
, page 57.
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 that the sensor is firmly attached to the horizontal section
of the hot water pipe, see
Fig. 76, page 56.
2. Check red wire connections at hot water 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
6.3, page 32 for
directions.
4. Check sensor (ref. page 45, chapter 9).
Display Cause Solution
Table 18
* By installer or service technician only.
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