BoilerFaultCodesYour boiler has stopped working because the water pressure in the central heating system is too low.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Check the system’s pressure and refill if necessary. Reset the boiler, if the fault reoccurs then you need to contact a heating engineer.
What causes this fault?
This fault occurs when the water levels inside your heating system drop below a safe operating limit, preventing the boiler from firing up to avoid damage. The most common reasons are a small leak somewhere in your radiator circuit or the need to bleed air from your radiators, which reduces the overall pressure. In some cases, a component inside the boiler like the expansion vessel may have failed, losing its ability to maintain steady pressure.
This fault is frequently seen in autumn when homeowners turn their heating back on for the first time after summer, revealing pressure drops that occurred while the system was idle.
DIY fix possible
Locate the filling loop (usually a silver braided hose with small valves underneath the boiler).Slowly open the valve(s) until you hear water entering the system and the pressure gauge reaches between 1 and 1.5 bar.Close the valves tightly and press the reset button on the boiler control panel.
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 AL40 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
Affiliate links — we may earn a commission at no extra cost to you.