F.318 High

Vaillant F.318 Fault Code

Also written as F318 — same fault.

The Vaillant F.318 fault code means: your boiler is struggling to switch between heating your radiators and heating your hot water because the internal valve that directs the water flow is not receiving an electrical signal.. It appears on 3 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: Fault in the electrical connection for the 3-port diverter valve. The 3-port motorised valve does not move.
Typical repair cost £180-350 (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.318 fault code

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

Source

Vaillant F.318 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 7 July 2026