BoilerFaultCodesIdeal System pressure below 0.4 bar Fault Code
Also written as SYSTEMPRESSUREBELOW04BAR — same fault.
The Ideal System pressure below 0.4 bar fault code means: your boiler has stopped working because the water pressure in the system has dropped too low.. It appears on 1 Ideal model in our database.
Technical description: The boiler will not operate. The heating system will need to be re-pressurised to at least 0.7bar
What causes the Ideal System pressure below 0.4 bar fault?
This fault occurs when there isn't enough water circulating inside your heating system to safely operate the boiler. The most common reasons are a slow leak from a radiator valve or pipework, or air being released from the system through the radiators. Over time, this loss of water lowers the internal pressure until the boiler's safety sensors shut the unit down to prevent internal damage.
This issue is more frequent in autumn or early winter when the heating is turned on for the first time after summer, as the change in temperature can reveal small leaks or trapped air.
DIY fix possible
Locate the filling loop (usually a silver flexible hose) under the boiler.Open the small valve taps until you hear water entering and the gauge reaches between 1.0 and 1.5 bar.Close both taps fully and restart the boiler.
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Gas Safe Register →Ideal models that show the System pressure below 0.4 bar fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal System pressure below 0.4 bar 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