BoilerFaultCodesWorcester Bosch P8 Fault Code
The Worcester Bosch P8 fault code means: your boiler has detected that the water pressure inside the system is too high, which can cause safety valves to leak or the unit to shut down.. It appears on 1 Worcester Bosch model in our database.
Technical description: High pressure
What causes the Worcester Bosch P8 fault?
This fault occurs when there is too much water in your heating system, placing excessive strain on internal components. The most common reason is that the filling loop has been left slightly open after topping up the pressure, though it can also happen if a component like the expansion vessel has failed and can no longer regulate water volume as it heats up.
This issue often appears at the start of autumn when homeowners bleed their radiators and accidentally overfill the system while preparing for the colder months.
DIY fix possible
Check that the filling loop valves are fully closedBleed a radiator to release excess water pressureMonitor the pressure gauge stays between 1 and 1.5 barEnsure the pressure relief valve is not dripping outside
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Gas Safe Register →Worcester Bosch models that show the P8 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch P8 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