Thermostat shows E05 and cannot control heating correctly

Safety first: Turn off mains power to the thermostat.

Steps:

• Remove the thermostat and locate the remote sensor terminals (often marked RS or similar).
• Check that the remote sensor wires are firmly secured and not pulled out or corroded.
• Use a multimeter to measure resistance across the remote sensor wires. Expect a reading in the kΩ range; OL or very high resistance indicates an open circuit.
• If the cable is damaged or the sensor is open, replace with a Heatmiser remote air sensor of the correct type.
• If you do not intend to use a remote sensor, disable it in the installer settings and select internal sensor mode only.