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Problem solving
39
(Flashing) Outlet temperature sensor not
sensing expected output
temperature.
1. Check that the sensor is firmly attached to the hot water pipe
(see Fig. 69, page 52).
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.
Primary fan rotation too low on
operation.
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.
70, page 53).
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.
No rotational speed sensor signal
from primary fan.
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.
70, page 53).
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.
1. Disconnect power supply cord and check wire connections on
water valve and the two connectors on the control board (see
Fig.
70, page 53).
2. Excessive water pressure and flow. Ensure water pressure is
less than 150psi and flow rate is below 10 gallons per minute.
Internal hardware/software failure. 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 ( ) to reset any error
codes.
3. Possible defective control unit. Call Bosch Water Heating for
further instructions.
Display Cause Solution
Table 20
* By installer or service technician only.