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Problem solving
Display
Cause
(Flashing)
Outlet temperature sensor not
sensing
temperature.
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.
Internal hardware/software failure.
Table 20
* By installer or service technician only.
42
Solution
1. Check that the sensor is firmly attached to the hot water pipe
expected
output
(see Fig.
2. Clean inlet filter screen and clear any debris out of shower
heads, faucet aerators and whole house filters.
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 prevent the heater
from reaching desired output temperature.
5. Check supply voltage. It must be 120VAC and properly
grounded.
6. Possible defective control unit call Bosch Water Heating for
further instructions.
7. Ensure that outlet temperature sensor is not placed on any
bends in the hot water pipe or misreading may occur.
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. 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
minimum 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 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.
1. Disconnect power supply cord and check the two wire and
ground connections on control board as well as ground connection
on heater chassis.
2. Pushing the wrong combination of buttons on the control unit
can create confusion among the microprocessors inside. In this
case, the error code should not happen more than once or twice.
Turn off the water heater. Turn water heater back on and try
resetting error code. Use the reset button (
codes.
3. Possible defective control unit. Call Bosch Water Heating for
further instructions.
70
55
, page
).
71
56
, page
).
71
56
, page
).
71
56
, page
).
) to reset any error
6 720 608 542
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