Thermostat displays E18 and cannot control whole-home humidifier connected to Amana furnace

Safety first: Turn off power to the furnace/air handler and humidifier at the breaker before working on wiring.

• Step 1 – Verify accessory configuration: In the thermostat installer menu, confirm that a humidifier is enabled and configured correctly (powered vs. non-powered, control type) according to Amana documentation.
• Step 2 – Inspect wiring at thermostat: Check the HUM/ACC terminals on the thermostat for secure connections and correct polarity if required.
• Step 3 – Inspect wiring at furnace/air handler: At the Amana control board, verify the humidifier is wired to the correct HUM or accessory terminals and that any external transformer is wired per the schematic.
• Step 4 – Test humidifier manually (advanced): Temporarily jumper the humidifier control leads per the Amana wiring diagram to see if the humidifier activates. If it does, the thermostat or its wiring is at fault.
• Step 5 – Replace thermostat: If wiring and configuration are correct and the humidifier works when manually activated, replace the thermostat.

When to call a professional: Humidifier wiring often involves both low and line voltage; have an HVAC technician handle this if you are not experienced.