BoilerFaultCodesYour boiler has shut down because it thinks the water inside is getting too hot or is not moving through the system properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flow temperature overheat lockout or no water flow lockout
What causes this fault?
This fault occurs when the water inside the boiler exceeds a safe temperature limit or isn't circulating correctly. The most common reasons are a failed pump that can't move the water, a blockage caused by sludge in the system, or a faulty sensor giving an incorrect temperature reading.
This issue is more frequent during the first cold snap of autumn when heating systems are turned on after being dormant all summer, which can cause internal pumps to seize.
DIY fix possible
Check that your radiator valves and any isolation valves are fully openEnsure your system pressure is topped up to between 1 and 1.5 barBleed your radiators to remove any trapped air and then reset 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 L1 — no call-out fees, no surprises.
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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.
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