E21 High

ECA E21 Fault Code

The ECA E21 fault code means: your boiler's main control computer is failing to process internal signals correctly, causing it to shut down for safety.. It appears on 1 ECA model 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: Analog to Digital Converter Failure
Typical repair cost £250-400 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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ECA models that show the E21 fault code

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

Source

ECA E21 fault code information on this page is sourced and cross-checked against the official ECA service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026