S.7 High

Vaillant S.7 Fault Code

Also written as S7 — same fault.

The Vaillant S.7 fault code means: your boiler is struggling to circulate water properly after turning off the heating, which is likely caused by a blockage or a pump issue.. It appears on 26 Vaillant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Heating mode – pump overrun error

What causes the Vaillant S.7 fault?

This fault occurs when the boiler's internal sensors detect that water isn't moving through the system quickly enough after the flames have gone out. The most common reasons are a failing circulation pump that can't push the water anymore, or a blockage caused by a build-up of sludge and debris in the pipework. Small mechanical parts like the check valve can also become stuck, physically preventing the water from flowing away from the heat exchanger.

This issue often surfaces in autumn when the heating is turned back on after a long summer break, as internal pump parts can seize up from lack of use.

Typical repair cost £180-450 (including labour)

Engineer required

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

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Vaillant models that show the S.7 fault code

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

Source

Vaillant S.7 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

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