How much does it cost to fix Vaillant error code Er.9?

Typical repair cost for the Vaillant Er.9 fault is £250-450 including labour.

Er.9 High

Vaillant Er.9 Fault Code

Q: What does the Vaillant Er.9 fault code mean?

Your boiler's electronic control system is failing to receive the correct power supply, preventing it from safely starting up for heating or hot water.

Also written as ER9 — same fault.

The Vaillant Er.9 fault code means: your boiler's electronic control system is failing to receive the correct power supply, preventing it from safely starting up for heating or hot water.. It appears on 2 Vaillant models in our database.

Technical description: Main transformer

Typical repair cost £250-450 (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.9 fault code

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

Source

Vaillant Er.9 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