BoilerFaultCodesWorcester Bosch P4 Fault Code
The Worcester Bosch P4 fault code means: your boiler is undergoing a startup sequence or a temporary software update and needs time to finish its internal checks.. It appears on 4 Worcester Bosch models in our database.
Technical description: Text display not yet defined
What causes the Worcester Bosch P4 fault?
These codes appear when the boiler's internal computer is running through its initial boot-up sequence or performing a temporary software update. They are typically seen after the power has been switched off and back on, or following a brief interruption in the electrical supply. It is the system's way of checking all safety sensors and settings before it begins the ignition process.
This code may be seen more frequently during winter months if local power outages or grid fluctuations occur due to heavy storms.
DIY fix possible
Wait up to 15 minutes for the sequence to completeDo not turn the power off during the updateObserve the display to see if it reverts to a normal temperature reading
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Gas Safe Register →Worcester Bosch models that show the P4 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch P4 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