E17 displayed and thermostat cannot detect or control external dehumidifier/humidifier accessory

Warning: Accessory circuits may carry 24VAC. Turn off power before wiring changes.

• Step 1 – Confirm accessory type:
  • Check whether your humidifier/dehumidifier requires a dry contact or 24VAC control signal.
  • Verify that the Gosund thermostat accessory output matches this requirement.
• Step 2 – Inspect wiring:
  • Ensure accessory wires are connected to the correct accessory terminals on the thermostat.
  • Check for shorts or loose connections.
• Step 3 – Test accessory independently:
  • Temporarily jumper the accessory’s control terminals (per manufacturer instructions) to confirm it operates.
  • If the accessory does not run when jumpered, the issue is with the accessory itself.
• Step 4 – Test thermostat accessory output:
  • With an accessory call active, measure voltage or continuity across the thermostat accessory terminals as specified in the manual.
  • If no output is present, the accessory driver circuit is likely defective.
• Step 5 – Replace thermostat if accessory port is bad:
  • Replace the thermostat if E17 persists and the accessory is known good and correctly wired.