BoilerFaultCodesVaillant S.05 Fault Code
Also written as S05 — same fault.
The Vaillant S.05 fault code means: your boiler is currently cooling itself down after a period of operation, which is a normal process and not actually a fault code.. It appears on 27 Vaillant models in our database.
Technical description: Fan and pump over run (837/637 only)
What causes the Vaillant S.05 fault?
This status occurs because your boiler needs to move heat away from its internal components after it has finished heating your home or hot water. The fan and pump continue to run for a short time to safely vent residual heat and prevent the unit from overheating. Once the internal temperature has dropped to a safe level, the boiler will return to its normal standby mode.
DIY fix possible
Wait for approximately 5 to 10 minutes for the cycle to complete.Ensure your room thermostat or programmer is calling for heat if the boiler does not restart.Check that your radiator valves are open to allow heat to dissipate.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Vaillant models that show the S.05 fault code
Click a model for the full fault code list and model-specific repair notes.
- aquaPLUS
- ecoTEC exclusive
- ecoTEC plus
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 65
- ecoTEC Plus 832
- ecoTEC Plus 836
- ecoTEC Plus 840
- ecoTEC Plus 938
- ecoTEC plus Aquaplus
- ecoTEC plus System
- ecoTEC Pro
- ecoTEC Pro 24
- ecoTEC Pro 28
- ecoTEC Pro 30
- ecoTEC sustain
- Home System
- Thermocompact
- Turbomax Plus 824/828E
- Turbomax Plus 828
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
Source
Vaillant S.05 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