Thermostat displays E3 and may disable heating; auxiliary or backup heat may not engage correctly.

Safety first: Shut off power to the air handler/ furnace and heat pump at the breaker before inspecting wiring.

• Check thermostat configuration: In installer settings, verify that the Payne smart thermostat is configured for the correct system type (heat pump with electric aux, heat pump with gas furnace, or conventional furnace). Incorrect configuration can trigger E3.
• Inspect W/AUX wiring: Remove the thermostat from the wall and confirm the W, W2, or AUX terminals are wired according to the Payne installation manual. Loose or broken conductors can cause the thermostat to detect an open circuit.
• Check at air handler/furnace: At the indoor unit, verify that the W/AUX terminal on the Payne control board is wired to the thermostat and that any high‑limit or aux heat sensor wiring is intact.
• Test aux heat operation: With power restored, command emergency heat or aux heat from the thermostat. Listen for relays clicking at the air handler. If nothing happens and E3 appears, the circuit is open or the thermostat driver is faulty.
• Sensor inspection (if equipped): Some Payne air handlers use a temperature sensor or limit switch on the electric heat kit. Inspect for loose connectors or tripped manual‑reset limits. Reset any manual limits per manufacturer instructions.
• Call a technician if unsure: Aux heat circuits carry higher current and are often 240V. If you are not experienced, have a professional test the aux heat kit and replace any failed sensors or the thermostat.