6 720 680 226
Problem solving
45
Exhaust temperature sensor - the
appliance will close the burner and
lock if it gets over 194°F; (only
applied for condensing unit).
1. Clean and check heat exchanger.
2. Clean and check condensing heat exchanger.
3. Reduce maximum power (
chapter 3.13
,
page 28
).
4. Reduce water temperature.
Backflow temperature sensor over
309°F.
The appliance will close the burner
and lock (non-volatile).
1. Check inlet/outlet vent pipes.
2. Check if secondary fan connections are disconnected.
3. Check if venting specifications are met. Long vent lengths,
venting with more than three elbows, blocked vent or combination
venting may cause this failure. See
chapter 3.3
,
page 9
.
4. Call Bosch Water Heating for further instructions.
Overheat sensor (ECO) open
circuit (resets when cooler
temperatures are detected 220
°
F/
104
°C
).
1. Disconnect power supply cord and check wire connections on
the overheat sensor (
Fig. 70
,
page 51
) and the two connectors
on the control board.
2. Check white wire connections at the overheat sensor. Clean
terminals with an eraser. If badly corroded, replace sensor and
wire harness.
3. Check that venting specifications are met. Long vent lengths,
venting with more than three elbows, blocked vent or combination
venting may cause this failure.
4. In areas where water has a high mineral content, periodic
descaling may necessary, see
chapter 6.3
,
page 35
.
5. 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.
No flame ionization detected with
water flow.
1. Verify that all manual gas shut off valves are open.
2. Check gas type. See
Fig. 2
,
page 6
.
3. Reset error code and open a water tap to cycle the heater in an
effort to purge air. Cycling hot water tap on and off multiple times
may be necessary. If heater still faults with EA error code, have a
licensed gas technician properly purge air out of the gas line
leading to the water heater.
4. Check three wire connections on the lower front of the heat
exchanger are secure.
5. Check gas pressure. See
chapter 3.13
,
page 28
.
6. Check venting specifications are met. Improper venting may
cause premature failure of the flame sensor rod. See
chapter 3.3
,
page 9
.
7. Check that the minimum power fan speed has been adjusted to
the proper value. See
page 16
.
8. Observe inside the viewing window of the heat exchanger when
a hot water tap is opened. Sparking should be followed by a
steady blue flame. If flame is unstable/yellow with proper gas
pressure, confirm CO2 readings per
chapter 6.5
,
page 36
.
Display Cause Solution
Table 20
* By installer or service technician only.
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