Bosch 520PN Applications Manual page 88

46 | Problem solving
Display Cause
Internal hardware/software failure.
Ionization error at standby.
Gas leakage error, gas valve circuit not
closing properly.
Table 39
* By installer or service technician only.
6 720 644 887 (2013/02)
Solution
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 (
error codes.
3. Possible defective control unit call Bosch Water Heating for further
instructions.
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.
1. Disconnect power supply cord and check wire connections on gas valve and
the two connectors on the control board.
2. Flow water out of a hot water tap above the minimum activation point of 0.5
GPM. Measure voltage at the gas valve wire plug connection. The voltage should
measure 24VDC between the left pair of wires and 24VDC between the right pair
of wires when the unit is operating. If voltage is not proper, contact Bosch Water
Heating for further instruction.
3. Gas valve may be defective, contact Bosch Water Heating for further
instruction.
) to reset any
C 1210 ES/ESC