Nest thermostat wiring terminals do not clamp or hold wires securely.

Safety: Turn off HVAC power before working on thermostat wiring.

• Use correct wire: Ensure you are using solid 18–22 AWG thermostat wire. If using stranded wire, tin the ends or use ferrules.
• Re-strip conductors: Cut back to clean copper and strip 3–4 mm of insulation.
• Test clamp action: Press the terminal button and insert the wire fully, then release and gently tug to confirm it is locked.
• Replace base: If terminals will not hold wires despite correct technique, the Nest base is defective and should be replaced (often as part of a new thermostat).