F.70 High

Vaillant F.70 Fault Code

Also written as F70 — same fault.

The Vaillant F.70 fault code means: your boiler’s internal computer boards are having trouble communicating because they haven't been properly synced or configured to recognize each other.. It appears on 44 Vaillant models 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: No valid appliance variant for display and/or electronics: Spare part case: Display and electronics changed at the same time appliance variant not re-set

What causes the Vaillant F.70 fault?

This fault occurs when the boiler's internal control boards fail to recognize the specific model they are installed in, often because the 'identity code' has been lost or not set. This usually happens after a physical repair where both the main circuit board and the display screen were replaced simultaneously, leaving the system without a master record of its own configuration. Without this data, the boiler enters a safety mode because it doesn't know its own power rating or technical specifications.

Typical repair cost £90-180 (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 F.70 fault code

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

Source

Vaillant F.70 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