Er.15 Medium

Vaillant Er.15 Fault Code

Also written as ER15 — same fault.

The Vaillant Er.15 fault code means: your boiler is struggling to detect when you turn on a hot tap, which means you may have no hot water or the water temperature might stay cold.. It appears on 1 Vaillant model 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: Aqua sensor
Typical repair cost £150-250 (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.15 fault code

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

Source

Vaillant Er.15 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