BoilerFaultCodesVaillant S.36 Fault Code
Also written as S36 — same fault.
The Vaillant S.36 fault code means: your temperature settings are too low for the boiler to start heating, so the system is currently on standby.. It appears on 25 Vaillant models in our database.
Technical description: Target value for ext. controller lower than 20°C: Reference setting for continuous controller 7-8-9 or eBUS controller is <20°C and blocks the heating mode
What causes the Vaillant S.36 fault?
This status occurs when the external thermostat is telling the boiler that the house is already warm enough, so the heating remains off. The boiler is physically capable of firing, but it is currently being 'blocked' or held in standby by the settings on your wall controller or smart app. This typically happens if the target temperature is set lower than the actual room temperature or if the thermostat batteries have failed.
This code is very common during spring and autumn when outdoor temperatures fluctuate, causing the thermostat to frequently reach its target and shut the heating down.
DIY fix possible
Check your wall thermostat or room controllerIncrease the temperature setting to above 20°CEnsure the thermostat is turned on and has working batteries
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Vaillant models that show the S.36 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £0-120
- ecoMAX
- ecoMAX 613 Repair: £0-120
- ecoMAX 618 Repair: £0-120
- ecoMAX 622 Repair: £0-120
- ecoMAX 635 Repair: £0-120
- Ecomax Condensing 600/800 series
- ecoMAX System 612 Repair: £0-120
- ecoTEC 65kW
- ecoTEC exclusive Repair: £0-60
- ecoTEC exclusive 627
- ecoTEC Plus 615 Repair: £0-120
- ecoTEC Plus 620 Repair: £0-120
- ecoTEC Plus 625 Repair: £0-120
- ecoTEC Plus 635 Repair: £0-120
- ecoTEC Plus 840 Repair: £0-120
- ecoTEC plus aquaPLUS Repair: £0-120
- Thermocompact
- Turbomax 824/828
- Turbomax Plus Repair: £80-150
- Turbomax Plus 824/828E
- Turbomax Plus 828 Repair: £60-180
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
Source
Vaillant S.36 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant Ecomax Condensing 600/800 series manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
- Vaillant ecoTEC 65kW manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026