A20
De Dietrich General Safety Lockout

Boiler shows A20, general safety lockout, no specific sub-code

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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

Multiple failed ignition attempts, Repeated overheating, Internal self‑diagnostic fault on De Dietrich control board, Combination of minor faults triggering lockout

How to Fix / Troubleshooting

Safety: Do not repeatedly reset a boiler that immediately locks out. Identify the underlying cause.

Steps:

  • Note conditions: Observe when A20 occurs (during DHW, heating, after long run). This helps identify the root cause.
  • Check for other codes: Some models store a history of previous errors. Access the diagnostic menu (installer level) to see which fault triggered the lockout.
  • Basic checks: Verify system pressure, flue integrity, and that all radiators/valves are open.
  • Single reset: Perform one reset and monitor operation. If A20 returns, stop using the boiler.

Professional help: A De Dietrich technician should perform a full diagnostic, including combustion analysis and electrical checks.

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Repair Difficulty

Hard 4/5
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