Parameter in memory not found
Internal Operations error
Internal memory parameter error
Internal memory error
Analog test fail
Gas type parameter error
Appliance parameter not defined
Burner Control routine state error
Burner Control error
Burner Control routine check sum error
Fan stopping error
Gas Control error
Ionization error at standby.
Gas leakage error, gas valve circuit not
* By installer or service technician only.
1. Replace ECU (Electronic Control Unit) if there are repeated errors.
1. Check primary fan cable harness
2. Check fan rotation in standby
3. Check proper function of primary fan
4. Replace ECU (Electronic Control Unit)
1. Check Gas Valve cable harness (connection to gas valve and to ECU)
2. Check Gas Valve (Replace if necessary)
3. Replace ECU (Electronic Control Unit)
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
2. Flame ionization rod or control unit may be damaged. Contact Bosch Water Heating for
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.
Problem solving | 53
6 720 805 440 (2014/11)