BoilerFaultCodesWorcester Bosch overheat lock-out state Fault Code
Also written as OVERHEATLOCKOUTSTATE — same fault.
The Worcester Bosch overheat lock-out state fault code means: your boiler has switched itself off because it has reached an internally high temperature and needs a manual restart to clear the safety lock.. It appears on 5 Worcester Bosch models in our database.
Technical description: Should the appliance not light, check it is not in the overheat lock-out state, by pressing the re-reset button on bottom right hand side of the control box.
What causes the Worcester Bosch overheat lock-out state fault?
This fault occurs when the water inside the boiler exceeds a safe temperature limit, triggering a safety switch to prevent damage. The most common reasons are a pump failure that stops water from moving through the system or a build-up of debris blocking the internal heat exchanger. It can also be caused by a faulty sensor misreading the temperature even if the boiler isn't actually too hot.
This fault is more common in autumn when heating systems are turned back on after a long summer break, often revealing a circulation pump that has seized during the idle months.
DIY fix possible
Locate the control box on the boiler unitIdentify the reset button on the bottom right-hand sidePress and hold the button for a few seconds to clear the lock-outCheck that your radiator valves are open to allow water to circulate
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Gas Safe Register →Worcester Bosch models that show the overheat lock-out state fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch overheat lock-out state 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