6 720 608 643
Problem solving
43
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 5.
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 26.
6. Check venting specifications are met. Improper venting may
cause premature failure of the flame sensor rod. See
chapter 3.12, page 16.
7. Check that the minimum power fan speed has been adjusted to
the proper value. See
page 19.
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 33.
Ionization failure during operation. 1. Check gas type,
Fig. 2, page 5.
2. Check three wire connections to ignition group on the lower
front of the heat exchanger are secure.
3. Verify that venting specifications are met. Improper venting may
cause premature failure of the flame sensor rod. See
chapter 3.12, page 16.
4. Check gas pressure. See chapter 3.13, page 26.
5. Check and adjust CO
2
readings. See chapter 6.5, page 33.
6. Check that the minimum power fan speed has been adjusted to
the proper value. See page 19.
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. Pressing 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.
Ionization error at standby. 1. Loose connection to the flame ionization rod. Verify that the
thinner wire leading from the control unit is securely connected to
the set of electrodes located on the lower front of the heat
exchanger.
2. Flame ionization rod or control unit may be damaged. Contact
Bosch Water Heating for further instruction.
Display Cause Solution
Table 18
* By installer or service technician only.
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