BoilerFaultCodesTechnical description
Fault codes 4x appear if the pressure in the boiler is low.
What causes this 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.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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