Heatmiser No Heat Demand Output

Thermostat is on but does not call for heat even when setpoint is higher than room temperature

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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

Incorrect control mode (cooling or off), Output relay not wired to boiler/wiring centre, Minimum off time or delay active, Faulty relay contacts

How to Fix / Troubleshooting

Safety first: Turn off power before checking wiring.

Steps:

  • Check the thermostat mode; ensure it is set to heating and not off or cooling.
  • Verify schedule: ensure the current time period is set to a temperature above room temperature.
  • At the thermostat, confirm that the call for heat output (e.g., NO/COM) is wired correctly to the Heatmiser wiring centre or boiler control input.
  • Use a multimeter to check for continuity across the relay contacts when the thermostat indicates heating is on. If no continuity, the relay may be faulty and the thermostat should be replaced.
  • Check installer settings for minimum on/off times or delays that may be preventing immediate activation.
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Repair Difficulty

Medium 3/5

Required Part

Heatmiser Smart Thermostat
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