How much does it cost to fix Vaillant error code S.2?

Typical repair cost for the Vaillant S.2 fault is £0-120 including labour.

S.2 Low

Vaillant S.2 Fault Code

Q: What does the Vaillant S.2 fault code mean?

Your boiler is preparing to heat your home and is checking that water is moving through the pipes before it lights the burner.

Also written as S2 — same fault.

The Vaillant S.2 fault code means: your boiler is preparing to heat your home and is checking that water is moving through the pipes before it lights the burner.. It appears on 26 Vaillant models in our database.

Technical description: Pump running – pre ignition (heating operation)

What causes the Vaillant S.2 fault?

This status occurs when the boiler's internal computer tells the pump to start moving water around your heating system in preparation for ignition. It is a normal part of the startup sequence where the boiler confirms there is sufficient water flow before it safely fires the burner. If the code stays on screen for a long time without the boiler firing, it may indicate that the pump is struggling to move water or the pressure sensor is having difficulty detecting the flow.

Typical repair cost £0-120 (including labour)

DIY fix possible

Check that your external heating controls or thermostat are set to 'On' and a high temperatureEnsure all radiator valves are open to allow water flowWait up to 10 minutes, as this is often a normal part of the boiler's start-up sequence

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Vaillant models that show the S.2 fault code

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

Source

Vaillant S.2 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