BoilerFaultCodesVokera 4x Fault Code
Also written as 4X — same fault.
The Vokera 4x fault code means: your boiler has detected that the water pressure is too low for it to operate safely and has shut down to protect the system.. It appears on 3 Vokera models in our database.
Technical description: Fault codes 4x appear if the pressure in the boiler is low.
What causes the Vokera 4x fault?
This fault occurs when the internal water pressure drops below the minimum level required for the boiler to circulate heat safely. It is usually caused by a small leak in the radiator system, air being bled from the radiators, or a failing component like the expansion vessel losing its charge.
This issue often appears in autumn when homeowners turn their heating back on for the first time, as the change in temperature and pressure can highlight small leaks or air pockets that developed over the summer.
DIY fix possible
Locate the filling loop (usually a silver braided hose under the boiler).Slowly open the valve or valves until you hear water entering the system.Watch the pressure gauge and close the valves once it reaches between 1.0 and 1.5 bar.Press the 'Reset' button on the control panel to restart the boiler.
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Gas Safe Register →Vokera models that show the 4x fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera 4x fault code information on this page is sourced and cross-checked against the official Vokera service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026