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 37 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.
Find a Gas Safe engineer
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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.
- Atmomax Repair: £150-£350
- ecoFIT Pure 418
- ecoFIT Pure 425
- ecoFIT Pure 435
- 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 824E Repair: £0-80
- ecoMAX 828E Repair: £0-80
- Ecomax Condensing 600/800 series
- ecoMAX System 612 Repair: £0-80
- ecoTEC
- ecoTEC exclusive Repair: £250-480
- ecoTEC Plus 826
- ecoTEC Plus 938
- ecoTEC plus aquaPLUS Repair: £0-120
- ecoTEC Pro
- ecoTEC Pro / ecoTEC Plus
- ecoTEC Pro 24
- ecoTEC Pro 28
- ecoTEC Pro 30
- ecoTEC sustain
- Home Combi
- Home System
- Thermocompact
- 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 manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026