BoilerFaultCodesVaillant F70 Fault Code
The Vaillant F70 fault code means: your boiler has lost its identity settings, meaning the internal computer no longer knows exactly which model it is controlling, which prevents it from operating.. It appears on 10 Vaillant models in our database.
Technical description: No valid DSN in display and/or main board
What causes the Vaillant F70 fault?
This fault occurs when the boiler's main control board and the display screen are not compatible or have not been properly introduced to each other. It usually happens after a repair where one of these parts was replaced but the unique software code for your specific boiler model wasn't entered. Without this identity code, the two components cannot communicate and the boiler will not fire up for safety reasons.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the F70 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 825 Repair: £120-250
- ecoTEC Repair: £150-300
- ecoTEC Plus 615 Repair: £250-450
- ecoTEC Plus 620 Repair: £80-120
- ecoTEC Plus 625 Repair: £80-120
- ecoTEC Plus 630 Repair: £80-120
- ecoTEC Plus 635 Repair: £150-300
- ecoTEC Plus 840 Repair: £150-300
- ecoTEC Plus 938 Repair: £150-300
- ecoTEC sustain Repair: £150-300
Source
Vaillant F70 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 825 manual (PDF)
- Vaillant ecoTEC manual (PDF)
- Vaillant ecoTEC Plus 840 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026