BoilerFaultCodesWorcester Bosch E00-721 Fault Code
Also written as E00721 — same fault.
The Worcester Bosch E00-721 fault code means: your boiler has detected a serious internal problem with the gas burner system, causing it to shut down for safety.. It appears on 1 Worcester Bosch model in our database.
Technical description: Burner Injector – Natural Gas Stereomatic, Type 7, Rs1/8 4.95mm
What causes the Worcester Bosch E00-721 fault?
This fault occurs when the boiler detects an unexpected signal from the burner, often suggesting gas is present when it shouldn't be or a sensor is malfunctioning. It is usually caused by a failing gas valve that isn't closing properly or a faulty set of electrodes failing to monitor the flame correctly. The system shuts down immediately as a safety precaution to prevent unburnt gas from building up.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Worcester Bosch models that show the E00-721 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch E00-721 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