BoilerFaultCodesYour boiler has detected that the water returning to the unit is too hot, which has caused it to shut down to prevent damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Return temperature sensor overheating due to a blocking fault or a lockout error – try resetting the boiler
What causes this fault?
This fault occurs when the water traveling back into the boiler from your radiators is at a higher temperature than the system expects, which usually signals a circulation problem. The most common reasons are a pump failure that isn't moving water fast enough, or a blockage caused by internal debris or air trapped in the system. As a safety measure, the boiler shuts down to prevent the internal components from being damaged by this excessive heat.
This issue is more common during the first cold spell of autumn, as circulation pumps can seize up after being inactive over the summer months.
DIY fix possible
Ensure all radiator valves are fully open to allow water to circulate.Check that the central heating system pressure is between 1.0 and 1.5 bar.Press the Reset button on the boiler control panel to clear the lockout.
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A boiler cover plan would cover faults like J6-20 — no call-out fees, no surprises.
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