BoilerFaultCodesVaillant d.34 Fault Code
Also written as D34 — same fault.
The Vaillant d.34 fault code means: your boiler is displaying the current fan speed for diagnostic purposes rather than an error, but it may indicate an issue with how the fan is communicating with the system.. It appears on 32 Vaillant models in our database.
Technical description: Value for the fan speed
DIY fix possible
Navigate the digital display to your main screenNo action is required as this is a diagnostic statusIf the boiler is not firing, try a single resetMonitor for actual error codes like F.32
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like d.34: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Vaillant models that show the d.34 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £200-£450
- ecoFIT Pure 418
- ecoFIT Pure 425 Repair: £180-450
- ecoFIT Pure 435
- ecoFIT Pure 825 Repair: £180-350
- ecoFIT Pure 830
- ecoFIT Pure 835
- ecoMAX
- ecoMAX 613
- ecoMAX 618
- ecoMAX 622
- ecoMAX 635
- Ecomax Condensing 600/800 series
- ecoMAX System 612
- ecoTEC 65kW Repair: £180-350
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 635
- ecoTEC Plus 840
- ecoTEC plus aquaPLUS Repair: £0-120
- ecoTEC sustain
- Home Combi Repair: £250-450
- Home System Repair: £0-120
- Thermocompact Repair: £180-350
- Turbomax 824/828 Repair: £150-300
- Turbomax Plus Repair: £180-350
- Turbomax Plus 824/828E Repair: £180-350
- Turbomax Plus 828 Repair: £150-300
- Turbomax Plus 828 E Repair: £180-350
- Turbomax Plus VUW 242E Repair: £150-350
- Turbomax Plus VUW 242EH Repair: £150-350
Source
Vaillant d.34 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 Ecomax Condensing 600/800 series manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026