Thermostat shows 'FLOOR HI' or similar warning and shuts off heating in underfloor mode.

Safety first: Isolate power to the underfloor heating system before working on wiring or actuators.

Steps to check:

• Check floor temperature setting: In the installer menu of the Salus underfloor thermostat (e.g. VS20WRF), verify the maximum floor temperature limit. Adjust to a safe but appropriate value (commonly 27–35°C for timber floors, higher for tile).
• Verify actual floor temperature: Feel the floor surface. If it is excessively hot, leave the system off and investigate the manifold and actuators for stuck valves or incorrect wiring that bypasses control.
• Inspect sensor placement: If accessible, confirm that the floor sensor is installed in a conduit between heating loops, not directly touching a heating cable or mat.
• Check sensor reading: With power off, measure the sensor resistance and compare to the expected value for the ambient floor temperature. A faulty sensor can falsely report high temperature.

Resolution: Correct any installation issues and replace the floor sensor if readings are incorrect. If the thermostat still reports 'FLOOR HI' with a known-good sensor and normal floor temperature, replace the thermostat.