L.320 High

Vaillant L.320 Fault Code

Also written as L320 — same fault.

The Vaillant L.320 fault code means: your boiler's water pump is struggling to spin, likely due to debris or inactivity, so the system is currently trying to clear itself to get your heating and hot water back on.. 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: Theheatingpumpisblocked.Theunitattemptstoloosentheblockage.
Typical repair cost £150-300 (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 L.320 fault code

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

Source

Vaillant L.320 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