BoilerFaultCodesWorcester Bosch Lockout light constantly on Fault Code
Also written as LOCKOUTLIGHTCONSTANTLYON — same fault.
The Worcester Bosch Lockout light constantly on fault code means: your boiler has switched itself off to prevent damage after detecting that it is getting too hot inside the unit.. It appears on 2 Worcester Bosch models in our database.
Technical description: Overheat thermostat trip. Possible causes: system not pressurised, air in system, bypass not fitted/adjusted, pump failure, or sensor/thermistor fault.
What causes the Worcester Bosch Lockout light constantly on fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety switch to shut the system down. The most common reasons are a lack of water pressure, a failing pump that isn't moving heat away from the boiler quickly enough, or trapped air pockets causing the unit to spike in temperature.
This issue often appears when the heating is first turned on in autumn, as circulation pumps can seize up after being idle throughout the summer.
DIY fix possible
Check the system pressure gauge and top up to 1.5 bar if lowEnsure all radiator valves are fully open to allow water to flowBleed any trapped air from your radiatorsPress the reset button after the boiler has cooled down
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Gas Safe Register →Worcester Bosch models that show the Lockout light constantly on fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch Lockout light constantly on 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