S.34 Low

Heatline S.34 Fault Code

Also written as S34 — same fault.

The Heatline S.34 fault code means: your boiler has detected that the external temperature is very low and has automatically turned itself on to heat the pipework and prevent it from freezing.. It appears on 8 Heatline models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: "Frost protection" mode

Engineer required

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

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Heatline models that show the S.34 fault code

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

Source

Heatline S.34 fault code information on this page is sourced and cross-checked against the official Heatline service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026