H. Medium

Halstead H. Fault Code

Also written as H — same fault.

The Halstead H. fault code means: your boiler has accidentally entered a testing mode used by engineers, meaning it is currently running at a very low power setting and may not heat your home or water effectively.. It appears on 2 Halstead models in our database.

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: SERVICE mode (flashing H.) - appliance runs at minimum CH output
Typical repair cost £80-150 (including labour)

Engineer required

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

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Halstead models that show the H. fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Halstead H. fault code information on this page is sourced and cross-checked against the official Halstead service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026