BoilerFaultCodesVaillant F70 Fault Code
The Vaillant F70 fault code means: your boiler's computer has lost its internal identification settings, preventing it from knowing how to operate correctly.. It appears on 2 Vaillant models in our database.
Technical description: Invalid product code (DSN)
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.
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.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026