BoilerFaultCodesWorcester Bosch 204 O Fault Code
Also written as 204O — same fault.
The Worcester Bosch 204 O fault code means: your boiler has stopped running because the water inside it has become hotter than the temperature you have requested.. It appears on 10 Worcester Bosch models in our database.
Technical description: Current primary water temperature higher than set value
What causes the Worcester Bosch 204 O fault?
This fault occurs when water is staying inside the boiler's heat exchanger for too long, causing it to overheat beyond the safe limit. The most common reasons are a pump failure that prevents water from moving around your radiators, or a blockage such as trapped air or sludge that is restricting the flow. Because the heat cannot be carried away from the boiler quickly enough, the system shuts down as a safety precaution.
This issue is more common during the first cold spell of autumn, when pumps that have sat idle all summer can seize up or struggle to restart.
DIY fix possible
Check that your radiator valves are open to allow water to circulateEnsure there is no air trapped in your radiators by bleeding themCheck that the boiler pressure gauge is between 1 and 1.5 barReset the boiler to see if the fault clears
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 204 O fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 204 O 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