BoilerFaultCodesYour boiler has lost water pressure and does not have enough water inside it 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: LACK OF WATER IN PRIMARY CIRCUIT: PERFORM WATER TOPPING - UP
What causes this fault?
This fault occurs when the water pressure inside your heating system drops below the minimum level required for the boiler to fire up. The most common reasons for this are a leak somewhere in your radiators or pipework, or a failure in the expansion vessel which helps manage pressure changes as the water heats up.
This issue often appears in autumn when the heating is turned on for the first time after summer, as the change in temperature can highlight minor leaks or a loss of pressure in the expansion vessel.
DIY fix possible
Locate the filling loop (the flexible silver hose) underneath or near your boilerSlowly open the one or two taps on the hose until you hear water flowingWatch the pressure gauge and close the taps once it reaches between 1.0 and 1.5 bar
Find a Gas Safe engineer
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A boiler cover plan would cover faults like 21 — no call-out fees, no surprises.
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Glow-worm Xtramax is discontinued — time for a new one?
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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