A10
De Dietrich
External Control / Thermostat Fault
Boiler shows A10, will not start, sometimes after wiring changes
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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
Open circuit room thermostat, faulty De Dietrich room controller, incorrect wiring on control terminals, broken low-voltage cable
How to Fix / Troubleshooting
Safety: Isolate power before working on control wiring. Low-voltage circuits can still be damaged by shorts.
- Check room thermostat: Ensure the De Dietrich room unit or external thermostat is powered and calling for heat. Replace batteries if applicable.
- Bypass test (qualified person): Temporarily link the boiler's room thermostat terminals (as per wiring diagram). If the boiler starts, the external control or its wiring is faulty.
- Inspect wiring: Check for damaged or loose cables between the boiler and the room controller.
- Technician tasks: A technician can test the low-voltage inputs on the main control PCB and replace the room controller or PCB if necessary.
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Repair Difficulty
Medium
3/5
Required Part
Room Thermostat / De Dietrich Room Controller
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