Thermostat displays E10 and cannot detect C-wire or loses power intermittently

Safety first: Turn off power to the furnace/air handler at the breaker before accessing the control board or thermostat wiring.

• Step 1 – Confirm C-wire presence: Remove the thermostat and check if a wire is connected to the C terminal on the sub-base. If not, the thermostat may be running on batteries or power stealing and may show E10.
• Step 2 – Check at furnace/air handler: Open the Amana unit’s control compartment and locate the low-voltage terminal strip. Confirm that the same color wire used for C at the thermostat is connected to the C terminal on the control board.
• Step 3 – Tighten connections: Tighten the C terminal screw at both the thermostat and control board. Ensure the conductor is fully under the clamp and not broken.
• Step 4 – Test continuity (advanced): With power off, disconnect the C wire at both ends and test continuity with a multimeter. If open, use a spare conductor in the thermostat cable as the new C wire and connect it at both ends.
• Step 5 – Evaluate transformer load: If multiple accessories (humidifier, zoning, etc.) are powered from the same 24V transformer, it may be overloaded. An HVAC technician may need to upgrade the transformer or add an auxiliary transformer.

When to call a professional: If you cannot identify the C terminal or suspect transformer issues, contact an HVAC technician.