b0
Miller
Blower On After Power Up / No Call for Heat
Miller furnace display shows b0; blower runs but no heat is produced.
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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
Stuck blower relay on control board, Miswired thermostat, Short between R and G terminals, Faulty control board
How to Fix / Troubleshooting
Safety: Turn off power before working on control wiring.
- Check thermostat wiring: At the furnace control board, verify that R, W, G, and Y wires are correctly landed and not shorted together. Remove the G wire; if the blower stops, the thermostat or wiring is calling for fan.
- Inspect thermostat settings: Ensure the fan mode is set to AUTO, not ON, if you do not want continuous fan.
- Test blower relay: If the blower runs even with the G wire removed and no call for heat or cool, the blower relay on the control board may be stuck closed. Replace the control board.
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Repair Difficulty
Medium
3/5
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