35 High

Vaillant 35 Fault Code

The Vaillant 35 fault code means: your boiler has encountered an internal diagnostic issue that requires a professional service technician to investigate and reset using specialized software.. It appears on 1 Vaillant model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Access code reserved for the customer service
Typical repair cost £120-250 (including labour)

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 35 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant 35 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 27 April 2026