BoilerFaultCodesVaillant F.65 Fault Code
Also written as F65 — same fault.
The Vaillant F.65 fault code means: your boiler's internal computer is overheating, which has caused the system to shut down to prevent damage to the electronics.. It appears on 46 Vaillant models in our database.
Technical description: PCB processor temperature too high | Check earth connection or electronics defect
What causes the Vaillant F.65 fault?
This fault occurs when the boiler's internal control center exceeds its safe operating temperature and shuts down to prevent the circuit board from melting or catching fire. It is usually caused by an electrical component failing on the board itself or excessive heat building up inside the boiler casing due to poor ventilation. In some cases, external heat source interference or a maturing electronic component can cause this overheating.
This fault is more common during the summer months or during heatwaves, as high ambient temperatures make it harder for the internal electronics to shed heat.
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.65: no call-out fees, no surprise bills.
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Vaillant models that show the F.65 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £180-350
- ecoFIT Pure 412 Repair: £180-350
- ecoFIT Pure 418 Repair: £150-300
- ecoFIT Pure 425 Repair: £150-300
- ecoFIT Pure 435 Repair: £150-300
- ecoFIT Pure 825 Repair: £200-450
- ecoFIT Pure 830 Repair: £150-300
- ecoFIT Pure 835 Repair: £150-300
- ecoMAX Repair: £220-450
- ecoMAX 613 Repair: £220-450
- ecoMAX 618 Repair: £220-450
- ecoMAX 622 Repair: £220-450
- ecoMAX 635 Repair: £220-450
- ecoMAX 824E Repair: £220-450
- ecoMAX 828E Repair: £220-450
- Ecomax Condensing 600/800 series Repair: £300-500
- ecoMAX System 612 Repair: £220-450
- ecoTEC Repair: £280-550
- ecoTEC 65kW Repair: £250-500
- ecoTEC exclusive Repair: £250-£550
- ecoTEC Plus 610 Repair: £250-500
- ecoTEC Plus 615 Repair: £250-450
- ecoTEC Plus 620 Repair: £250-450
- ecoTEC Plus 625 Repair: £250-450
- ecoTEC Plus 630 Repair: £250-450
- ecoTEC Plus 635 Repair: £250-450
- ecoTEC Plus 826 Repair: £250-450
- ecoTEC Plus 840 Repair: £250-450
- ecoTEC Plus 938 Repair: £250-450
- ecoTEC plus aquaPLUS Repair: £250-450
- ecoTEC Pro Repair: £250-450
- ecoTEC Pro / ecoTEC Plus Repair: £180-450
- ecoTEC Pro 24 Repair: £250-450
- ecoTEC Pro 28 Repair: £250-450
- ecoTEC Pro 30 Repair: £250-450
- ecoTEC sustain Repair: £250-450
- Home Combi Repair: £150-350
- Home System Repair: £250-450
- Thermocompact Repair: £250-£450
- Turbomax 824/828 Repair: £250-450
- Turbomax Plus Repair: £250-450
- Turbomax Plus 824/828E Repair: £180-350
- Turbomax Plus 828 Repair: £280-450
- Turbomax Plus 828 E Repair: £180-350
- Turbomax Plus VUW 242E Repair: £180-350
- Turbomax Plus VUW 242EH Repair: £180-350
Source
Vaillant F.65 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