BoilerFaultCodesWorcester Bosch G5 Fault Code
The Worcester Bosch G5 fault code means: your boiler has failed to ignite or stay lit correctly, meaning it cannot provide heating or hot water until it is reset or repaired.. It appears on 1 Worcester Bosch model in our database.
Technical description: Fault burner
What causes the Worcester Bosch G5 fault?
This fault occurs when the boiler's control system cannot detect a steady flame after trying to ignite. The most common reasons are a worn-out sensor that monitors the flame, a build-up of carbon on the sparking electrodes, or a fault with the gas valve that prevents fuel from reaching the burner.
This fault is frequently seen during the first cold snap of autumn when internal components that have been idle over summer fail to operate correctly under increased demand.
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 G5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch G5 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