A04
De Dietrich
Control Board / Configuration Fault
Boiler shows A04 and will not start, sometimes after power interruption
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Corrupted control board parameters, incompatible or faulty control PCB, wiring harness fault
How to Fix / Troubleshooting
Safety: Isolate power before touching internal wiring. Electronic work should be done by a qualified technician.
- Power cycle: Turn off the boiler at the main switch for 2–3 minutes, then turn it back on. Sometimes the control board resets.
- Check external controls: Disconnect external room thermostat or OpenTherm controller (if fitted) and try running the boiler in basic mode to rule out communication issues.
- Inspect wiring harness: With power off, visually inspect the main harness to the control board for loose plugs, burnt connectors, or damaged insulation. Reseat connectors firmly.
- Technician tasks: A De Dietrich service engineer can reload parameters, update firmware, or replace the main control PCB if it is defective.
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Repair Difficulty
Professional Required
5/5
Required Part
Main Control PCB
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