Thermostat shows E6 and cannot complete normal operation; may be accompanied by frozen screen or unresponsive buttons.

Safety first: Disconnect power or remove batteries before attempting resets.

Steps to check:

• Hard reset: Remove the thermostat from its base and take out the batteries (if battery-powered). For mains models, isolate power at the breaker. Leave unpowered for at least 5 minutes, then restore power and check if E6 clears.
• Factory reset: Access the installer or advanced menu and perform a factory reset according to the Salus manual. This can clear corrupted configuration data.
• Check for recent updates: If the thermostat is an internet-connected model (e.g. Salus iT500, RT310i, Smart Home series), check in the app or web portal for any failed firmware update messages. Avoid interrupting power during updates.
• Test basic functions: After reset, test manual temperature changes and schedule programming. If the unit remains unstable or repeatedly shows E6, internal memory is likely damaged.

Resolution: Persistent E6 after resets indicates a hardware-level memory or MCU fault. Replace the thermostat head or gateway as appropriate. Firmware re-flashing is typically not user-serviceable.