BoilerFaultCodesYour heating system has shut down because it is struggling to circulate water properly while detecting very cold temperatures within the unit.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: High Flow/Return Differential, 3 times in succession and Flow Temperature <7°C
What causes this fault?
This fault occurs when the boiler detects that water is not moving through the system quickly enough to carry heat away, combined with an internal temperature that is dangerously close to freezing. The most common reason is a blockage in the pipework or a failing pump that prevents the water from circulating. Because the water is sitting still in freezing conditions, the boiler shuts down to prevent the internal pipes from cracking due to ice expansion.
This fault is almost exclusively seen during the winter months, as it requires both a circulation issue and an external temperature low enough to drop the unit's internal water below 7°C.
DIY fix possible
Check that all radiator valves are fully openEnsure the system pressure is between 1 and 1.5 barCheck for any frozen external condensate or heat pump pipes
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