E05
Delta Dore Relay Output Fault in RF Receiver or Wired Relay Module

Thermostat shows E05 and cannot control the boiler; receiver output does not switch when there is a heat demand.

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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

Stuck relay contacts in Delta Dore receiver, Burned relay due to overcurrent, Incorrect wiring on COM/NO terminals, Internal receiver PCB damage

How to Fix / Troubleshooting

Safety first: Turn off power to the boiler and receiver at the main switch or breaker before opening the receiver housing.

  • Visual inspection: Open the Delta Dore receiver (e.g. Tybox receiver near the boiler). Check for burn marks, melted plastic, or a burnt smell around the relay area.
  • Check wiring: Verify that the boiler control wires are correctly connected to the COM and NO (or NC if specified) terminals as per the Delta Dore wiring diagram. Tighten any loose screws.
  • Manual test: Put the thermostat into a high setpoint (e.g. 30°C) and observe the receiver LED and relay click. If the LED indicates demand but the boiler does not start, the relay may be stuck or open.
  • Reset receiver: Press and hold the receiver’s reset or PROG button for several seconds to reset it, then re-pair with the thermostat. Test again.

If the relay is physically damaged or not switching despite correct signals, the receiver module should be replaced. Relay replacement on the PCB is not recommended for non-professionals.

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Repair Difficulty

Hard 4/5

Required Part

Delta Dore RF Receiver Relay Module
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