BoilerFaultCodesIdeal P5 Fault Code
The Ideal P5 fault code means: your boiler has detected that water is struggle to circulate through your heating system quickly enough, often due to a blockage or a pump issue.. It appears on 1 Ideal model in our database.
Technical description: High Flow/Return Differential
What causes the Ideal P5 fault?
This fault occurs when the water temperature leaving the boiler is significantly higher than the water returning, suggesting that heat isn't being moved away fast enough. The most common cause is a restriction in the system, such as a build-up of sludge in the heat exchanger or a failing pump that can no longer push water through the radiators effectively.
This issue is most frequently seen during the first cold spell of autumn when the heating is turned back on after sitting idle for several months, often causing the pump to seize.
DIY fix possible
Ensure all radiator valves (TRVs) are turned to the highest settingCheck that the boiler pressure is between 1 and 1.5 barBleed all radiators to remove trapped air from the system
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Gas Safe Register →Ideal models that show the P5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal P5 fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026