BoilerFaultCodesYour boiler has detected that the water inside is not circulating properly or there is air trapped in the system, causing it to stop 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: Clas net one / Clas one CombiClas system one
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water is moving too slowly or not at all, which risks overheating the internal components. The most common reasons are a buildup of sludge blocking the pipes, air trapped within the system, or the internal pump failing to push water around your radiators.
This code often appears when the heating is turned back on for autumn, as the pump can seize or debris can settle during the summer months of inactivity.
DIY fix possible
Check if your boiler pressure is between 1 and 1.5 bar on the gauge.Attempt to bleed any air from your radiators using a radiator key.Restart the boiler by pressing the Reset button to see if the fault clears.
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