T.04 High

Vaillant T.04 Fault Code

Also written as T04 — same fault.

The Vaillant T.04 fault code means: your boiler is struggling to move heated water to your hot water cylinder, which means you may not have any 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: Cyl. charging pump

What causes the Vaillant T.04 fault?

This fault occurs when the boiler is unable to detect that water is being successfully moved to heat your hot water cylinder. The most common reason is that the dedicated charging pump has either seized up due to debris or suffered an electrical failure, preventing the transfer of heat. In some cases, a loose wiring connection or a faulty control board means the pump isn't receiving the signal to start.

Typical repair cost £180-£350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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.04 fault code

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

Source

Vaillant T.04 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