Aprilaire whole-home dehumidifier (e.g., models 1830, 1850, 1870) displays E1 on the onboard control

Safety first: Disconnect power to the dehumidifier at the service switch or breaker before removing panels.

• Access control compartment: Remove the access panel to expose the main control board and sensor harnesses.
• Locate return sensor: The return air temperature sensor is typically mounted near the return air inlet or on the evaporator coil, connected by a small two-wire harness to the board.
• Check connection: Ensure the sensor plug is fully seated on the correct board header. Reseat the connector several times to clean contacts.
• Inspect wiring: Look for cuts, pinches, or pulled wires along the harness path.
• Test sensor: Disconnect the sensor and measure resistance across its leads. Compare to Aprilaire’s thermistor chart for the ambient temperature. If reading is open or far out of range, the sensor is defective.
• Replace sensor: Install a new Aprilaire return air temperature sensor (thermistor), route the harness away from sharp edges, and secure it.
• Restore power and test: Reinstall panels, restore power, and confirm the E1 code clears and the unit operates.