Google Nest
Low Power / Charging Failure
Nest thermostat reboots frequently or shows a red blinking light
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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
No C wire and marginal power draw from HVAC, Loose R connection, Undersized or failing transformer, Excessive load from additional accessories on R/C
How to Fix / Troubleshooting
Safety warning: Turn off HVAC power at the breaker before modifying wiring.
- Verify C wire presence: If no C wire is connected, consider adding one from the furnace control board C terminal to the Nest C terminal.
- Secure R and C connections: Ensure both R and C wires are firmly seated at the Nest base and at the furnace control board.
- Reduce accessory load: If multiple devices (humidifier, Wi‑Fi modules, zone boards) share the same transformer, consider adding a dedicated transformer or Nest Power Connector.
- Check transformer rating: Confirm the 24V transformer is sized appropriately (typically 40 VA or higher for modern systems with smart thermostats).
Persistent rebooting after correcting power issues may indicate a failing Nest internal battery, requiring display replacement.
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Repair Difficulty
Medium
3/5
Required Part
Nest Thermostat Base, Nest Power Connector, HVAC 24V Transformer
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