Medium
C (Flashing) on Halstead Ace 100

Your boiler has accidentally switched into a low-power maintenance mode meant only for technicians, meaning it is currently providing much less heat than usual.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

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

The appliance enters the SERVICE mode (runs at minimum CH output).

Engineer required

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

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