BoilerFaultCodesVaillant F.11 Fault Code
Also written as F11 — same fault.
The Vaillant F.11 fault code means: your boiler's electronic control systems have stopped talking to each other, which prevents the unit from starting or running your heating and hot water.. It appears on 47 Vaillant models in our database.
Technical description: No reception by main board Connection fault between main PCB and interface; Faulty interface; Faulty main PCB (processor
What causes the Vaillant F.11 fault?
This fault occurs when the boiler's internal sensors detect a massive temperature difference between the water entering and leaving the unit, usually because the water has stopped moving. The most common reason is a failed internal pump or a heavy buildup of sludge and debris blocking the main heat exchanger. Without proper flow, the water inside the unit reaches a boiling point almost instantly, forcing the system to shut down for safety.
This issue is most frequently seen during the first cold snap of autumn when a boiler is switched back on after being idle all summer, often causing a seized pump to finally give up.
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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A cover plan would handle faults like F.11: no call-out fees, no surprise bills.
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Vaillant models that show the F.11 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £150-450
- 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: £150-350
- ecoMAX System 612 Repair: £90-160
- ecoTEC Repair: £100-£180
- ecoTEC 65kW Repair: £150-250
- ecoTEC exclusive Repair: £90-180
- 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 826 Repair: £120-220
- ecoTEC Plus 840 Repair: £100-£180
- ecoTEC Plus 938 Repair: £100-£180
- ecoTEC plus aquaPLUS Repair: £90-180
- 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 Combi Repair: £120-200
- Home System Repair: £100-£180
- Thermocompact Repair: £90-160
- Turbomax 824/828 Repair: £120-220
- Turbomax Plus Repair: £120-220
- 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.
- Vaillant ecoFIT Pure 412 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant ecoMAX manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026