E03
De Dietrich External Safety Circuit Open

Boiler shows E03, external safety device open (e.g., flue thermostat, safety chain)

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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 manual reset safety thermostat on De Dietrich boiler, External safety interlock (e.g., flue gas sensor) tripped, Broken wire in safety loop, Incorrect wiring of external safety devices

How to Fix / Troubleshooting

Safety: Identify why the safety device opened before resetting. Do not bypass safety circuits.

Steps:

  • Locate safety devices: Identify all thermostats and safety switches wired in series with the boiler (e.g., flue thermostat, high‑limit thermostat).
  • Check reset buttons: Once the boiler has cooled, press any manual reset buttons on safety thermostats until they click.
  • Inspect wiring: Look for loose or broken wires in the safety chain.
  • Reset boiler: After restoring the safety loop, reset the boiler and monitor operation.

Professional help: If a safety device trips repeatedly, a technician must investigate the underlying cause (overheating, flue blockage, etc.).

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Repair Difficulty

Hard 4/5

Required Part

Safety Thermostat
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