BoilerFaultCodesYour boiler has stopped running because it failed to light properly or has become too hot, causing it to lock itself for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Ignition lockout or boiler overheat
What causes this fault?
This fault happens when the boiler tries to light but fails to detect a stable flame, or if the internal temperature rises too fast and triggers a safety switch. It is usually caused by a lack of gas reaching the burner, worn-out sparking components, or a pump failure that prevents heat from moving away from the boiler. To protect itself from damage, the system shuts down completely until the issue is resolved.
This issue is frequently seen during the first cold snap of autumn when internal components like the pump or gas valve seize up after being idle throughout the summer.
DIY fix possible
Check if your gas supply is active (e.g., check other gas appliances like a hob)Ensure the system pressure is between 1.0 and 1.5 bar on the pressure gaugePress and hold the reset button for five seconds to restart the boiler
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 FLASHING SLOW (once per second) — no call-out fees, no surprises.
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Worcester Bosch 24si II 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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