i4 Low

Worcester Bosch i4 Fault Code

Also written as I4 — same fault.

The Worcester Bosch i4 fault code means: this code is not actually an error; it is simply showing you the current maximum heating power level for your hot water production.. It appears on 1 Worcester Bosch model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Maximum DHW output - The maximum possible DHW output is displayed in kW.

Engineer required

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

Find a Gas Safe engineer

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Worcester Bosch models that show the i4 fault code

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

Source

Worcester Bosch i4 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