Meross
False Heat Demand / Ghost Firing
Thermostat causes the boiler to fire even when no heating demand is expected (e.g., in OFF mode).
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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
Backfeed voltage on control line from other controls, Miswired COM/NO/NC contacts, Stuck or leaking relay contacts
How to Fix / Troubleshooting
Safety first: Turn off power to both thermostat and boiler before inspecting wiring.
Steps:
- Check control wiring diagram: Ensure the thermostat's COM and NO (or NC) are wired correctly to the boiler's control terminals. Remove any parallel connections with other thermostats unless designed for it.
- Isolate thermostat: Disconnect the thermostat control wires at the boiler. If the boiler stops firing unexpectedly, the thermostat or its wiring is the cause.
- Test relay contacts: With the thermostat powered off and removed, measure continuity between COM and NO. There should be no continuity when off. If continuity exists, the relay is leaking or stuck.
Resolution: Correct wiring to prevent backfeed and replace the thermostat if the relay contacts are not fully opening.
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Repair Difficulty
Hard
4/5
Required Part
Heating Control Relay
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