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 46 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
Search the official register for a qualified engineer in your area.
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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.
- 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 612 Repair: £90-180
- ecoFIT pure 615 Repair: £90-180
- ecoFIT pure 618 Repair: £90-180
- ecoFIT pure 630 Repair: £90-180
- ecoFIT Pure 825 Repair: £120-220
- ecoFIT Pure 830 Repair: £120-200
- ecoFIT Pure 835 Repair: £120-220
- ecoFIT sustain 415 Repair: £120-220
- ecoFIT sustain 418 Repair: £120-220
- ecoFIT sustain 430 Repair: £120-220
- ecoFIT sustain 615 Repair: £90-180
- ecoFIT sustain 618 Repair: £90-180
- ecoFIT sustain 630 Repair: £90-180
- ecoFIT sustain 825 Repair: £90-180
- ecoFIT sustain 830 Repair: £90-180
- ecoFIT sustain 835 Repair: £90-180
- 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 824/2 E Repair: £90-160
- ecoMAX 828/2 E Repair: £90-160
- ecoMAX 835 E Repair: £90-160
- Ecomax Condensing 600/800 series Repair: £120-220
- ecoMAX Pro 28E Repair: £150-350
- ecoTEC exclusive Repair: £90-180
- ecoTEC plus Repair: £100-£180
- ecoTEC plus VU GB 656/4-5 A Repair: £150-250
- ecoTEC pro Repair: £90-160
- ecoTEC sustain Repair: £100-£180
- Home Combi 25 Repair: £120-200
- Home Combi 30 Repair: £120-200
- Home Combi 35 Repair: £120-200
- Home Regular 12
- 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 425 manual (PDF)
- Vaillant ecoFIT Pure 435 manual (PDF)
- Vaillant ecoFIT pure 630 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026