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Problem solving
43
8
Problem solving
8.1
Error code diagnostics
i
To remove error code from the
display, press the reset button.
Display
Cause
Solution
Fault in the flue gas limiter.
Temperature above 230°F (110°C)
inside the cabinet.
1. Check continuity of the flue gas limiter (see
Fig. 70
,
page 51
).
Go to steps two and three to determine flue gas limiter fault and
repair it.
2. Check for flue gas leakage around the top and bottom seals of
heat exchanger, use mirror to check around the rear as well as the
viewing window.
3. Check that flue gas limiter connector and spade connections
are secure.
4. Unplug heater and check the wiring harness connections on the
control board.
Exhaust temperature sensor -
happens if sensor is disconnected
or in short circuit or appliance
selection on “P7” mode is not
correct.
1. Check exhaust temperature sensor connection. See
Fig. 70
,
#1,
page 51
.
2. Check sensor (ref.
page 48
,
chapter 10
).
3. Check “P7” mode: water heater requires setting “Cd” for
condensing appliances
.
Backflow
temperature
sensor
defect - happens if sensor is
disconnected or short circuit.
1. Check backflow temperature sensor connection. See
Fig. 70
,
#1,
page 51
.
2. Replace exhaust temperature sensor.
3. Check sensor (ref.
page 48
,
chapter 10).
Outlet temperature sensor fault
(Temperature below 36°F or above
210°F).
1. Check red wire connections at hot water temperature sensor.
Clean terminals with an eraser. If badly corroded, replace sensor
and wire harness. See
Fig. 65
,
page 47
.
2. Sensor may trip if water temperature drops below 36°F to
protect heater from freezing conditions. Any damage due to
freezing conditions is not covered under warranty.
3. In areas where water has a high mineral content, periodic
descaling may necessary.
4. Check sensor (ref.
page 48, chapter 10).
(Flashing)
Outlet temperature sensor not
sensing
expected
output
temperature.
(Status message, not an error).
1. Check that the sensor is firmly attached to the vertical section of
the hot water pipe, see
Fig. 76
,
page 58
.
2. Ensure that hot water sensor is not placed on any bends in the
hot water pipe or misreading may occur.
3. Check gas pressure. Low gas pressure may prevent the heater
from reaching desired output temperature.
4. Check supply voltage. It must be 120VAC and properly
grounded.
5. Possible defective control unit call Bosch Water Heating for
further instructions.
Table 20
* By installer or service technician only.
