S.76 Low

Vaillant S.76 Fault Code

Also written as S76 — same fault.

The Vaillant S.76 fault code means: your boiler is warning you that the water pressure is getting too low to operate efficiently, though it may still be working for now.. It appears on 5 Vaillant 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: Service message: Check water pressure. A service message is activated. Check the water pressure.

What causes the Vaillant S.76 fault?

This message is triggered when the internal sensor detects that the system's water pressure has dropped below the ideal operating level. It is usually caused by a small leak in the pipework, air being bled from radiators, or a component like the expansion vessel losing its charge. Because the pressure is low, the boiler is struggling to circulate heat effectively around your home.

This warning is more frequent in autumn and winter when homeowners turn their heating back on after a long break or bleed their radiators to remove cold spots.

Typical repair cost £0-80 (including labour)

DIY fix possible

Locate the filling loop valves underneath the boilerSlowly open both valves until you hear water movingMonitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then close both valves tightly

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Vaillant models that show the S.76 fault code

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

Source

Vaillant S.76 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