T.02 High

Vaillant T.02 Fault Code

Also written as T02 — same fault.

The Vaillant T.02 fault code means: your boiler is struggling to switch between providing hot water and heating your radiators because an internal valve is stuck or malfunctioning.. It appears on 12 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: 3-way valve

What causes the Vaillant T.02 fault?

This fault occurs when the mechanical component that directs hot water between your taps and radiators becomes jammed or fails to move. It is often caused by a build-up of debris and sludge from within the heating system or a simple failure of the small motor that pushes the valve into position.

This issue is frequently noticed in autumn when homeowners turn their heating back on for the first time, as the valve may have seized after months of only providing hot water.

Typical repair cost £180-£320 (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 T.02 fault code

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

Source

Vaillant T.02 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