E9 221 High

Worcester Bosch E9 221 Fault Code

Also written as E9221 — same fault.

The Worcester Bosch E9 221 fault code means: your boiler has detected that a critical safety sensor is disconnected or faulty, so it has safely shut itself down to prevent overheating.. It appears on 1 Worcester Bosch 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: Safety sensor open circuit - Maximum temperature sensor on the main heat exchanger has not been recognised.
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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Worcester Bosch models that show the E9 221 fault code

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

Source

Worcester Bosch E9 221 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026