T.08 Low

Vaillant T.08 Fault Code

Also written as T08 — same fault.

The Vaillant T.08 fault code means: your boiler is currently completing a routine check of its burner system while it is in the process of starting up.. It appears on 12 Vaillant models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Burner

What causes the Vaillant T.08 fault?

This message appears because the internal control board is performing a brief safety verification of the gas burner's functionality during the ignition sequence. It is a completely normal part of the boiler's startup procedure used to ensure the system is operating correctly before it begins heating. This is not a physical failure or a breakdown, but rather a standard status update from the boiler's software.

DIY fix possible

Wait for 2-5 minutes to see if the status code clears automaticallyCheck that your gas supply is active at the meterEnsure your thermostat is calling for heat

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Vaillant models that show the T.08 fault code

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

Source

Vaillant T.08 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