S.96 Low

Vaillant S.96 Fault Code

Also written as S96 — same fault.

The Vaillant S.96 fault code means: your boiler is performing a self-diagnostic check on its internal temperature sensors and has temporarily paused heating until it confirms everything is working correctly.. It appears on 25 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: Return temperature sensor self-test: Return sensor test running, heating demands are blocked.

What causes the Vaillant S.96 fault?

This occurs when the boiler's control system notices an unusual discrepancy between the temperature readings of the flow and return pipes. To ensure the heat exchanger doesn't overheat, the boiler pauses operation to run a quick test and verify that the internal sensors are reporting accurate data. It is often triggered by air bubbles trapped in the system or a pump that is beginning to struggle with water circulation.

This can be more frequent in autumn when the heating is turned on for the first time after summer, as air often settles in the pipework during the warmer months.

Typical repair cost £0-120 (including labour)

DIY fix possible

Wait up to 15 minutes for the automated test to completeSwitch the boiler off and back on at the fused spur switch to trigger a restartEnsure all radiator valves are open to allow for proper water circulation

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Vaillant models that show the S.96 fault code

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

Source

Vaillant S.96 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