Display shows E17; furnace may not respond to thermostat or room controller.

Safety: Turn off power before working on low-voltage control wiring.

• Check thermostat wiring: Inspect the two-core cable from the room thermostat or Kospel controller to the furnace terminals. Tighten loose screws and repair damaged cable.
• Bypass test (if allowed): Temporarily bridge the thermostat terminals at the furnace to simulate a heat demand. If the furnace starts, the thermostat or its wiring is faulty.
• Verify settings: Ensure the thermostat is set to heating mode and the setpoint is above room temperature.

If E17 remains even with a bypass, the control board input may be defective and require replacement.