BoilerFaultCodesYour boiler has detected that the water isn't moving through the system correctly, causing a large temperature gap between the pipes.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Different temperature between flow and return
What causes this fault?
This fault occurs when the boiler detects that water is leaving the unit much hotter than it is when it returns, suggesting the water is stuck or moving too slowly. The most common reasons are a failing internal pump that can't push the water around, or a blockage caused by a buildup of sludge and debris in the system or heat exchanger.
This issue often surfaces in autumn when the heating is turned back on after the summer, as the pump can seize or debris can settle during the months of inactivity.
DIY fix possible
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air bubbles
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