Thermostat displays E15 and indicates C-wire or power stealing error; may run on batteries only if equipped

Safety first: Turn off power to the furnace/air handler at the breaker before adding or changing any thermostat wiring.

Steps to resolve E15 C-wire fault:

• 1. Confirm C terminal at furnace: Open the Goodman furnace/air handler panel and locate the control board. Identify the C terminal and verify a wire is connected and firmly secured.
• 2. Verify C at thermostat: Ensure the same conductor is landed on the C terminal at the thermostat. Label wires if necessary to avoid confusion.
• 3. Add C wire if missing: If no spare conductor is available in the thermostat cable, consider pulling a new 5–8 conductor cable or using a Goodman-approved C-wire adapter module at the furnace.
• 4. Check for shared transformers: If multiple systems share the same thermostat, ensure their transformers are properly phased and commons are tied together per Goodman and accessory manufacturer instructions.
• 5. Remove unauthorized adapters: Remove any third-party power-stealing devices that may interfere with proper C-wire detection.
• 6. Power up and test: Restore power and verify that the thermostat no longer reports E15 and remains powered with the display stable.