BoilerFaultCodesWorcester Bosch P3 Fault Code
The Worcester Bosch P3 fault code means: your boiler is currently running a self-cleaning routine to remove trapped air bubbles from the internal pipes and pump.. It appears on 10 Worcester Bosch models in our database.
Technical description: Appliance is in Air purge mode, see service function 2.C.
What causes the Worcester Bosch P3 fault?
This occurs when air becomes trapped within the boiler's heat exchanger or pump, often following a recent repair or system refill. The boiler automatically detects this air and triggers a programmed sequence to pulse the pump and vent the bubbles safely to ensure efficient operation. It isn't a mechanical failure, but rather a protective routine to prevent the system from overheating.
This code is more common in autumn when homeowners first switch their heating back on or bleed their radiators after a long period of disuse.
DIY fix possible
Wait for the timer to count down; the process usually takes 2 to 10 minutes.Ensure your radiator valves are open to help move air through the system.Check the pressure gauge is between 1 and 1.5 bar; top up if it has dropped.
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Worcester Bosch models that show the P3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch P3 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
- Worcester Bosch 537i manual (PDF)
- Worcester Bosch ZB 7 27 HE manual (PDF)
- Worcester Bosch ZWB 7-25 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026