BoilerFaultCodesIdeal P4 Fault Code
The Ideal P4 fault code means: your heat pump has stopped working because its internal system is getting too hot, usually due to a lack of water flow or a refrigerant issue.. It appears on 1 Ideal model in our database.
Technical description: Compressor Discharge Temperature High
What causes the Ideal P4 fault?
This fault occurs when the gas leaving the compressor becomes dangerously hot, which usually happens because heat isn't being moved away from the unit quickly enough. The most common cause is restricted water flow through the system due to a failing pump or a blockage, but it can also be triggered if the unit is leaking refrigerant.
This fault is more common during summer heatwaves or periods of very high demand for hot water, as the system has to work harder to reject heat.
DIY fix possible
Check that all radiator valves and zone valves are fully openEnsure the external unit is clear of leaves, debris, or snow blocking airflowCheck your system pressure gauge and top up to 1.5 bar if it is too low
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Gas Safe Register →Ideal models that show the P4 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal P4 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