309 Low

Worcester Bosch 309 Fault Code

The Worcester Bosch 309 fault code means: your boiler is currently operating exactly as it should be, as this code simply indicates it is busy heating your radiators and hot water.. It appears on 2 Worcester Bosch models 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: CH & DHW system are being heated

Engineer required

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

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Worcester Bosch models that show the 309 fault code

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

Source

Worcester Bosch 309 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