BoilerFaultCodesVaillant F.11 Fault Code
Also written as F11 — same fault.
The Vaillant F.11 fault code means: your boiler has stopped working because it thinks the water returning to the unit is much hotter than it actually is, causing it to shut down for safety.. It appears on 53 Vaillant models in our database.
Technical description: Return NTC short circuit. NTC defective, short circuit in cable harness, cable/casing short cut
What causes the Vaillant F.11 fault?
This fault occurs when the sensor responsible for monitoring the temperature of water coming back into the boiler develops an electrical short circuit. The most common reason is that the sensor itself has suffered an internal failure or natural wear and tear, leading it to send an incorrect signal to the main control board. In some cases, water damage or a loose connection within the internal wiring can also cause this electrical error.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Vaillant models that show the F.11 fault code
Click a model for the full fault code list and model-specific repair notes.
- aquaPLUS Repair: £90-180
- Atmomax Repair: £150-450
- Combi Compact 242EB Repair: £120-£350
- Combi Compact 282EB Repair: £90-280
- ecoFIT pure Repair: £120-220
- ecoFIT Pure 412 Repair: £150-250
- ecoFIT Pure 418 Repair: £120-220
- ecoFIT Pure 425 Repair: £120-220
- ecoFIT Pure 435 Repair: £120-220
- ecoFIT Pure 825 Repair: £120-220
- ecoFIT Pure 830 Repair: £120-200
- ecoFIT Pure 835 Repair: £120-220
- ecoMAX Repair: £100-180
- ecoMAX 613 Repair: £90-160
- ecoMAX 618 Repair: £90-160
- ecoMAX 622 Repair: £90-160
- ecoMAX 635 Repair: £90-160
- ecoMAX 824E Repair: £90-160
- ecoMAX 828E Repair: £90-160
- Ecomax Condensing 600/800 series Repair: £120-220
- ecoMAX Pro 28E Repair: £180-£350
- ecoMAX System 612 Repair: £90-160
- ecoTEC Repair: £100-£180
- ecoTEC exclusive Repair: £90-180
- ecoTEC plus Repair: £100-£180
- ecoTEC Plus 610 Repair: £120-200
- ecoTEC Plus 615 Repair: £100-£180
- ecoTEC Plus 620 Repair: £100-£180
- ecoTEC Plus 625 Repair: £100-£180
- ecoTEC Plus 630 Repair: £100-£180
- ecoTEC Plus 635 Repair: £100-£180
- ecoTEC Plus 65 Repair: £100-£180
- ecoTEC Plus 826 Repair: £120-220
- ecoTEC Plus 832 Repair: £100-£180
- ecoTEC Plus 836 Repair: £100-£180
- ecoTEC Plus 840 Repair: £100-£180
- ecoTEC Plus 938 Repair: £100-£180
- ecoTEC plus Aquaplus Repair: £120-220
- ecoTEC plus Regular Repair: £120-200
- ecoTEC plus System Repair: £120-220
- ecoTEC Pro Repair: £90-160
- ecoTEC Pro / ecoTEC Plus Repair: £90-160
- ecoTEC Pro 24 Repair: £90-160
- ecoTEC Pro 28 Repair: £90-160
- ecoTEC Pro 30 Repair: £120-220
- ecoTEC sustain Repair: £100-£180
- Home System Repair: £100-£180
- Thermocompact Repair: £90-160
- Turbomax Plus 824/828E Repair: £120-200
- Turbomax Plus 828 Repair: £120-£200
- Turbomax Plus 828 E Repair: £120-200
- Turbomax Plus VUW 242E Repair: £120-200
- Turbomax Plus VUW 242EH Repair: £120-200
Source
Vaillant F.11 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