S.97 Low

Vaillant S.97 Fault Code

Also written as S97 — same fault.

The Vaillant S.97 fault code means: your boiler is performing a routine internal check on its water pressure sensor and should resume normal operation once finished.. It appears on 21 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: Water pressure sensor self-test. The self-test for the water pressure sensor is activated.

What causes the Vaillant S.97 fault?

This occurs when the boiler's internal computer performs a safety check to ensure it is receiving an accurate reading from the water pressure sensor. It happens automatically to verify that the system is not running dry, which protects the internal components from overheating. Most often, this is just a momentary pause in operation, but if it persists, it may indicate the sensor is sending inconsistent signals or the wiring has become loose.

Typical repair cost £130-220 (including labour)

DIY fix possible

Wait up to 15 minutes for the automated test to completeCheck if the water pressure is between 1.0 and 2.0 barReset the boiler if the code remains on the screen for a prolonged period

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Vaillant models that show the S.97 fault code

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

Source

Vaillant S.97 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