Thermostat shows E2 and cannot detect a valid C-wire or power adapter; screen may dim or reboot.

Safety first: Turn off power to the HVAC system at the breaker before working on low-voltage wiring.

• Confirm presence of a C-wire: Remove the Wyze thermostat display and check if a wire is connected to the C terminal on the wall plate. If no C-wire is present, you must use the Wyze C-Wire Adapter or run a new C conductor.
• Inspect C-wire at furnace: At the furnace/air handler control board, locate the C terminal. Ensure the same colored wire used at the thermostat is securely attached here.
• Verify Wyze C-Wire Adapter wiring: If using the Wyze adapter, confirm that the adapter is wired exactly as shown in the Wyze installation guide: the four thermostat wires (Y, G, R, W) go into the adapter, and the adapter’s leads go to the corresponding terminals on the control board plus C. Any misplacement will cause E2.
• Check for damaged cable: Gently tug each conductor at the thermostat and furnace ends. If a wire pulls out easily or shows corrosion or breaks, the thermostat cable may need repair or replacement.
• Restore power and test: After correcting wiring, restore power, reattach the thermostat, and wait several minutes. The E2 code should clear once stable 24VAC between R and C is detected.