Medium
1 16 on Ariston Clas HE 24

Your boiler has detected that the external temperature safety switch—typically used for underfloor heating—is triggered or disconnected, preventing the system from running safely.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

floor thermostat contact open

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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