Problem Solving - Bosch 940 ESO Installation Manual

11

Problem solving

11.1 Error code diagnostics
To remove error code from the
i
display, press the reset button.
Display Cause
Fault in the flue gas limiter.
Temperature
(110°C) inside the cabinet.
Appliance selection on "P7" mode
is not correct.
Backflow
defect - happens if sensor is
disconnected or short circuit.
Outlet temperature sensor fault
(Temperature below 36°F or above
210°F).
Table 12
* By installer or service technician only.
6 720 644 956
Solution
1. Check continuity of the flue gas limiter (see Fig.
above 230°F Go to steps two and three to determine air box temperature
sensor fault and replace 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 inside
the control board.
1. Check "P7" mode: the
2. Check jumper and connection on sensor at upper right hand
corner of heat exchanger.
3. Measure jumper resistance, must be 115-125 ohms.
temperature sensor 1. Check blackflow temperature sensor connection. See
page
2. Replace backflow temperature sensor.
3. Check sensor (ref.
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.
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 be necessary.
4. Check sensor (ref.
water heater
47
.
page 45 chapter 13
,
65
, page
page 44 chapter 13
,
Problem solving
65 47
, page
requires setting "NC".
Fig. 65
).
47.
).
).
,
39