Display shows E6 and thermostat cannot control external sensor

Safety first: Turn OFF power at the breaker before accessing wiring.

Steps to troubleshoot:

• 1. Identify external sensor terminals:
  • Remove the thermostat from the wall and locate the external sensor or limit sensor terminals (often separate from the floor NTC terminals).
• 2. Check wiring:
  • Ensure both sensor wires are firmly connected and not reversed (polarity usually does not matter for NTC, but both must be connected).
  • Look for damaged insulation or crushed cable where it enters the wall.
• 3. Measure sensor resistance:
  • Disconnect the external sensor wires and measure resistance with a multimeter.
  • Compare with the expected value for the sensor type (e.g. 10 kΩ at 25°C for NTC 10k).
  • If reading is open (OL) or near 0 Ω, the sensor is faulty.
• 4. Replace external sensor if needed:
  • Install a new Heatit external room sensor or compatible NTC sensor as specified in the manual.
  • Route the cable away from mains cables to reduce interference.
• 5. Configure sensor in menu:
  • In the installer menu, enable the external sensor and select the correct type.
  • Save settings and verify that E6 clears.