Baxi Stuck Heating Relay / Permanent Call for Heat

Heating stays on constantly even when thermostat is set low or turned off.

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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

Welded relay contacts in Baxi receiver, Miswired COM/NO/NC terminals, Shorted control cable at boiler, Faulty boiler control board ignoring thermostat

How to Fix / Troubleshooting

Safety first: Turn off power at the fused spur before opening the receiver or boiler wiring compartment.

Steps to diagnose:

  • 1. Turn thermostat to OFF: Set the thermostat to OFF or a very low temperature and confirm it shows no heat demand.
  • 2. Observe receiver: The heating demand LED should be off. If the boiler still runs, the relay may be stuck or wiring misconfigured.
  • 3. Inspect wiring: Check that the boiler’s room thermostat terminals are wired via the receiver’s COM and NO (or as specified), not permanently bridged.
  • 4. Test relay contacts: With power off, disconnect the control wires from the receiver and check continuity between COM and NO. There should be no continuity when the relay is at rest. Continuity indicates welded contacts.
  • 5. Temporary safe state: If heating is stuck on and you cannot repair immediately, isolate the boiler at the fused spur to stop heating until a professional attends.

When to call a professional: A stuck relay or boiler control fault requires component replacement by a qualified engineer.

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Repair Difficulty

Hard 4/5

Required Part

Baxi smart thermostat receiver module
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