T.05 High

Vaillant T.05 Fault Code

Also written as T05 — same fault.

The Vaillant T.05 fault code means: your boiler's internal pump is having trouble moving water through the system, which is preventing it from providing heating or hot water.. 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: Circulation pump

What causes the Vaillant T.05 fault?

This fault occurs when the boiler's internal pump fails to circulate water effectively through the heat exchanger. The most common reasons are a mechanical failure of the pump motor, a buildup of sludge blocking the internal components, or air trapped within the unit preventing the pump from turning.

This fault is frequent in autumn when heating systems are switched back on after a summer of inactivity, which can cause the pump to seize.

Typical repair cost £220-450 (including labour)

DIY fix possible

Check that your system pressure is between 1.0 and 1.5 bar on the digital displayEnsure all radiator valves and isolation valves under the boiler are fully openBleed your radiators to remove any trapped air that might be blocking water flow

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Vaillant models that show the T.05 fault code

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

Source

Vaillant T.05 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