E01-603 High

Worcester Bosch E01-603 Fault Code

Also written as E01603 — same fault.

The Worcester Bosch E01-603 fault code means: your boiler's built-in pressure tank is no longer able to manage the expansion of water as it heats up, which is causing your system pressure to fluctuate and force the boiler to shut down.. 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: Expansion Vessel (8Ltr)
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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Worcester Bosch models that show the E01-603 fault code

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

Source

Worcester Bosch E01-603 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 7 July 2026