BoilerFaultCodesYour boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The system pressure has dropped below 0.5 bar and the boiler will not light.
What causes this fault?
This fault occurs when the water pressure inside your heating system drops below a safe working level, causing the boiler to shut down to prevent damage. The most common reasons for this are a leak somewhere in your radiators or pipework, or a failure of the internal expansion vessel which helps manage pressure changes.
This issue often appears when you turn your heating back on for the first time in autumn, as the system cools and contracts during the summer months.
DIY fix possible
Locate the silver filling loop underneath or near the boiler.Slowly open the valve or valves until you hear water entering the system.Close the valves once the pressure gauge on the front of the boiler reaches between 1.0 and 1.5 bar.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like P 0.4 — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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