Ruud
No Call for Heat Recognition
Boiler does not respond to thermostat call; thermostat appears to work but boiler stays 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
Broken thermostat wire, incorrect thermostat type, failed low‑voltage transformer, defective input circuit on control board
How to Fix / Troubleshooting
Safety first: Turn off power before working on low‑voltage wiring.
- Verify thermostat settings: Ensure the thermostat is set to HEAT and the setpoint is above room temperature.
- Check wiring at boiler: Confirm thermostat wires are securely connected to the correct terminals.
- Test with jumper: With power off, remove thermostat wires and install a temporary jumper between the call‑for‑heat terminals. Restore power. If the boiler starts, the thermostat or its wiring is faulty.
- Check transformer output: A technician can measure 24 VAC output from the transformer. If absent, replace the transformer.
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Repair Difficulty
Medium
3/5
Required Part
24V Control Transformer
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