Er.13 Medium

Vaillant Er.13 Fault Code

Also written as ER13 — same fault.

The Vaillant Er.13 fault code means: your boiler is struggling to switch between heating your radiators and heating your hot water taps, which may cause your hot water to stop working or your radiators to get hot when they shouldn't.. It appears on 2 Vaillant models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Diverter valve
Typical repair cost £180-280 (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 Er.13 fault code

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

Source

Vaillant Er.13 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