BoilerFaultCodesVaillant S.16 Fault Code
Also written as S16 — same fault.
The Vaillant S.16 fault code means: your boiler has detected an issue with the air fan system and has temporarily stopped heating to prevent further damage.. It appears on 26 Vaillant models in our database.
Technical description: DHW mode: Fan overrun
What causes the Vaillant S.16 fault?
This fault occurs when the boiler's control system detects that the fan is spinning but sending back incorrect signals, or it isn't spinning at the speed required for safe combustion. The most common reason is an internal electrical failure within the fan motor itself or a communication glitch between the fan and the main circuit board. Without the fan functioning perfectly to clear exhaust gases, the boiler shuts down as a safety precaution.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the S.16 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 825
- ecoFIT Pure 830
- ecoFIT Pure 835
- ecoMAX
- ecoMAX 613 Repair: £0-80
- ecoMAX 618 Repair: £0-80
- ecoMAX 622 Repair: £0-80
- ecoMAX 635 Repair: £0-80
- ecoMAX 824/2 E Repair: £0-80
- ecoMAX 828/2 E Repair: £0-80
- ecoMAX 835 E Repair: £0-80
- Ecomax Condensing 600/800 series
- ecoTEC exclusive Repair: £250-480
- ecoTEC plus
- 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.16 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 835 manual (PDF)
- Vaillant Ecomax Condensing 600/800 series manual (PDF)
- Vaillant ecoMAX 835 E manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026