BoilerFaultCodesVaillant S.88 Fault Code
Also written as S88 — same fault.
The Vaillant S.88 fault code means: your boiler is currently running an automatic air removal process to clear bubbles from the system and does not require a repair.. It appears on 28 Vaillant models in our database.
Technical description: Purging programme is running. The purge programme is activated.
What causes the Vaillant S.88 fault?
This occurs when your boiler detects air trapped within the internal heat exchanger or pipework, often following a service, a repair, or after the system has been drained and refilled. The boiler automatically pauses its normal heating cycle to run the pump and internal valves to push these air bubbles toward the automatic air vent. Once the system is satisfied that the air has been purged, the boiler will return to normal operation on its own.
This code is most common in autumn when homeowners turn their heating back on for the first time or after summer maintenance work has been carried out on the radiators.
DIY fix possible
Wait approximately 5 to 7 minutes for the cycle to complete automaticallyEnsure your radiator valves are open to help move air through the systemCheck that the system pressure is between 1.0 and 1.5 bar on the display
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Vaillant models that show the S.88 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
- ecoFIT Pure 835
- ecoFIT sustain 615
- ecoFIT sustain 618
- ecoFIT sustain 630
- ecoTEC exclusive 627
- ecoTEC plus 412
- ecoTEC plus 415
- ecoTEC plus 418
- ecoTEC plus 424
- ecoTEC plus 430
- ecoTEC Plus 610
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 832
- ecoTEC Plus 840
- ecoTEC Pro
- ecoTEC Pro / ecoTEC Plus
- ecoTEC sustain
- Home Combi
- Home System
Source
Vaillant S.88 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 835 manual (PDF)
- Vaillant ecoFIT sustain 630 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026