Bosch Evolution 500 Instruction Manual page 43

Display Cause
Over-temperature
outlet temperature sensor on hot
water pipe.
Temperature > 185°F
Cold water temperature sensor
fault.
Backflow temperature sensor over
309°F.
The appliance will close the burner
and lock.
Overheat
circuit (should reset when cooler
temperatures are detected).
Table 20
* By installer or service technician only.
6 720 680 223
Solution
detected by 1. Check that the sensor is firmly attached to the vertical section of
the hot water pipe (see Fig.
2. Check red wire connections at outlet temperature sensor.
Clean terminals with an eraser. If badly corroded, replace sensor
and wire harness. Check sensor resistance (see
46
3. Clean inlet filter screen per chapter
debris out of shower heads, faucet aerators and whole house
filters.
4. In areas where water has a high mineral content, periodic
descaling may be necessary. See chapter
directions.
1. Check connector on wires coming from top of watervalve for a
secure connection. See Fig.
2. Sensor may trip if water temperature drops below freezing to
protect heater from freezing conditions Any damage due to
freezing conditions is not covered under warranty.
1. Check combustion air and backflow vent piping for blockage.
2. Check if secondary fan connections are disconnected.
3. Check venting specifications are met.
venting with more than three elbows, blocked vent or combination
venting may cause this failure.
4. Check sensor resistance (see
sensor (ECO) open 1. Disconnect power supply cord and check wire connections on
overheat sensor (top right of heat exchanger) and the two
connectors on the control board. See Fig.
2. Check white wire connections at overheat sensor. Clean
terminals with an eraser. If badly corroded, replace sensor and
wire harness.
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. Clean inlet filter screen and clear any debris out of shower
heads, faucet aerators and whole house filters.
5. In areas where water has a high mineral content, periodic
descaling may necessary, see
6. Unplug power supply cord to the water heater. Open a hot
water tap for several minutes to allow cold water to pass through
heat exchanger. Close hot water tap and disconnect lead wires to
overheat sensor. Using a multimeter, check continuity through
overheat sensor contacts. Replace sensor if open.
70
.
64
Problem solving
55
, page ).
Fig. 60
6.2 page 32
, and clear any
6.3 page 32
,
49.
, page
Long vent lengths,
Fig. 62 page 47
, ).
64 49.
, page
chapter 6.3
.
page
,
for
43