BoilerFaultCodesYour boiler has experienced a sudden technical error and has locked itself to prevent damage, requiring a manual reset to attempt to clear the fault.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Volatile lockout
What causes this fault?
This fault occurs when the boiler's internal computer detects a critical failure during the ignition process or a sudden loss of flame during operation. The most common reasons are worn-out ignition components failing to spark or the gas valve not delivering the correct amount of fuel to the burner.
This fault is slightly more common in winter, as cold weather can put additional strain on aging ignition components and gas valves.
DIY fix possible
Press and hold the 'Reset' button for five secondsWait for the blue light to stop flashing and stay solidCheck if your gas supply is active (e.g. check a gas hob or prepay meter credit)
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 Fast flash, Lockout reset: Off — no call-out fees, no surprises.
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Worcester Bosch Greenstar 25Si 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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