Nest
Intermittent Power Drop / Firmware Instability
Nest thermostat reboots randomly or frequently restarts during heating or cooling
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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
Weak 24V supply due to missing or loose C wire, Failing internal battery unable to hold charge, Overloaded transformer shared with many devices, Corrupted firmware or software bug
How to Fix / Troubleshooting
Safety: Turn off HVAC power before adjusting wiring.
- Verify C wire: Ensure a dedicated C wire is connected from the furnace control board to the Nest base. If none exists, consider installing a Nest Power Connector.
- Tighten connections: Check that R and C wires are firmly clamped at both the Nest base and furnace control board.
- Update firmware: Connect the Nest to a stable Wi‑Fi network and allow it to update to the latest firmware.
- Measure voltage under load: Use a multimeter to check R‑C voltage while the system is running. If it dips significantly, the transformer may be undersized or failing.
- Replace thermostat: If power is stable and firmware is current but reboots continue, the internal battery or main board may be defective and the Nest should be replaced.
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Repair Difficulty
Medium
3/5
Required Part
Nest Thermostat (Internal Battery / Main Board)
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