BoilerFaultCodesVaillant F.27 Fault Code
Also written as F27 — same fault.
The Vaillant F.27 fault code means: your boiler has detected a signal error between its control system and gas supply, preventing it from lighting safely.. It appears on 68 Vaillant models in our database.
Technical description: No demand to gas valve | Cause: Electronic board defective, Gas valve defective
What causes the Vaillant F.27 fault?
This fault occurs when the boiler's internal computer detects a flame signal at a time when there shouldn't be one, or if the sensors are providing conflicting information. The most common reason is a communication failure between the electronic control board and the gas valve, causing the system to shut down as a safety precaution. In some cases, moisture or a failing component can trick the boiler into thinking gas is burning when the valve is actually closed.
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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Vaillant models that show the F.27 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £150-350
- ecoFIT Pure 412 Repair: £150-300
- ecoFIT Pure 418 Repair: £180-350
- ecoFIT Pure 425 Repair: £180-350
- ecoFIT Pure 435 Repair: £180-350
- ecoFIT pure 612
- ecoFIT pure 615
- ecoFIT pure 618
- ecoFIT pure 630
- ecoFIT Pure 825 Repair: £150-300
- ecoFIT Pure 830 Repair: £150-300
- ecoFIT Pure 835 Repair: £180-350
- ecoFIT sustain 415
- ecoFIT sustain 418
- ecoFIT sustain 430
- ecoFIT sustain 615
- ecoFIT sustain 618
- ecoFIT sustain 630
- ecoFIT sustain 825
- ecoFIT sustain 830
- ecoFIT sustain 835
- ecoMAX Repair: £150-350
- ecoMAX 613 Repair: £250-£550
- ecoMAX 618 Repair: £250-£550
- ecoMAX 622 Repair: £250-£550
- ecoMAX 635 Repair: £250-£550
- Ecomax Condensing 600/800 series Repair: £150-300
- ecoMAX System 612 Repair: £250-£550
- ecoTEC Repair: £120-350
- ecoTEC 65kW Repair: £150-350
- ecoTEC exclusive Repair: £150-350
- ecoTEC exclusive 627
- ecoTEC plus 412 Repair: £150-350
- ecoTEC plus 415 Repair: £150-350
- ecoTEC plus 418 Repair: £150-350
- ecoTEC plus 424 Repair: £150-350
- ecoTEC plus 430 Repair: £150-350
- ecoTEC Plus 610 Repair: £150-350
- ecoTEC plus 612
- ecoTEC Plus 615 Repair: £150-350
- ecoTEC plus 618
- ecoTEC Plus 620 Repair: £150-350
- ecoTEC plus 624
- ecoTEC Plus 625 Repair: £150-350
- ecoTEC Plus 630 Repair: £150-350
- ecoTEC Plus 635 Repair: £150-350
- ecoTEC plus 637 Repair: £120-350
- ecoTEC Plus 826 Repair: £150-300
- ecoTEC Plus 832 Repair: £150-350
- ecoTEC Plus 840 Repair: £150-350
- ecoTEC Plus 938 Repair: £150-300
- ecoTEC plus aquaPLUS Repair: £180-450
- ecoTEC Pro Repair: £120-250
- ecoTEC Pro / ecoTEC Plus Repair: £120-350
- ecoTEC Pro 24 Repair: £120-250
- ecoTEC Pro 28 Repair: £120-250
- ecoTEC Pro 30 Repair: £150-300
- ecoTEC sustain Repair: £150-350
- Home Combi Repair: £150-300
- Home System Repair: £120-£350
- Thermocompact Repair: £180-450
- Turbomax 824/828 Repair: £200-450
- Turbomax Plus Repair: £200-450
- Turbomax Plus 824/828E Repair: £200-450
- Turbomax Plus 828 Repair: £180-450
- Turbomax Plus 828 E Repair: £200-450
- Turbomax Plus VUW 242E Repair: £200-450
- Turbomax Plus VUW 242EH Repair: £200-450
Source
Vaillant F.27 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 835 manual (PDF)
- Vaillant ecoFIT pure 630 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026