BoilerFaultCodesVaillant 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 31 Vaillant models in our database.
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.
- ecoFIT Pure 412
- ecoFIT Pure 418
- ecoFIT Pure 425
- ecoFIT Pure 435
- ecoFIT Pure 825
- ecoFIT Pure 830 Repair: £120-250
- ecoFIT Pure 835
- ecoMAX
- ecoMAX 613
- ecoMAX 618
- ecoMAX 622
- ecoMAX 635
- ecoMAX 824/2 E
- ecoMAX 828/2 E
- ecoMAX 835 E
- Ecomax Condensing 600/800 series
- ecoTEC exclusive
- ecoTEC plus
- ecoTEC plus VU GB 656/4-5 A
- ecoTEC pro
- ecoTEC sustain
- Home Combi 25
- Home Combi 30
- Home Combi 35
- Turbomax 824/828
- Turbomax Plus
- Turbomax Plus 824/828E
- Turbomax Plus 828
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
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.
- Vaillant ecoFIT Pure 425 manual (PDF)
- Vaillant ecoFIT Pure 435 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026