Miller
No Call Reaching Control / Low-Voltage Circuit Failure
Furnace will not start at all; thermostat is calling for heat but nothing happens.
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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, Blown 3–5A control fuse, Failed 24V transformer, Faulty thermostat
How to Fix / Troubleshooting
Safety: Turn off power before testing low-voltage circuits to avoid shorting the board.
- Check control fuse: Inspect the automotive-style fuse on the Miller control board. Replace with the same rating if blown and look for shorts in thermostat wiring.
- Test transformer output: With power on, measure 24V AC between R and C at the control board. If no voltage, test and replace the 24V transformer.
- Bypass thermostat: Temporarily jumper R to W at the control board. If the furnace starts, the thermostat or its wiring is faulty and should be repaired or replaced.
- Inspect wiring: Look for broken or chewed thermostat wires, especially in crawlspaces or wall cavities.
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Repair Difficulty
Medium
3/5
Required Part
24V Transformer
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