S.28 Low

Vaillant S.28 Fault Code

Also written as S28 — same fault.

The Vaillant S.28 fault code means: your boiler has temporarily stopped the burner because it has reached the required temperature for hot water and is taking a short break to prevent overheating.. It appears on 41 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: Hotwaterhandlingmode:Temporaryshutdownoftheburner

What causes the Vaillant S.28 fault?

This occurs when your boiler successfully heats the water in the plate heat exchanger to the set temperature and temporarily switches off the burner to prevent waste. It is a normal part of the boiler's operation, indicating that the system is simply waiting for the water temperature to drop slightly before firing up again to maintain a steady flow. This prevents the unit from overheating and ensures a consistent temperature at your taps.

This code may be more noticeable in summer when the incoming mains water is naturally warmer, meaning the boiler reaches its target temperature much faster than in winter.

DIY fix possible

Check that your hot water taps are fully closedWait for 5 to 10 minutes for the 'S' status code to clear automaticallyMonitor the boiler to see if it moves into a heating or standby state

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Vaillant models that show the S.28 fault code

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

Source

Vaillant S.28 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