BoilerFaultCodesYour boiler has detected that heat is building up too quickly and cannot circulate around your home, likely due to a blockage or a pump failure.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: DIFF GREATER THAN 50°C CHECK ISOLATION VALVES ARE OPEN CHECK PUMP CHECK RAD VALVES OPEN CHECK SYSTEM BLOCKAGES
What causes this fault?
This fault occurs when the temperature difference between the water leaving the boiler and the water returning to it becomes too high, usually because the water isn't moving fast enough. The most common reason is a failed internal pump or a physical blockage in the system, such as a build-up of sludge or closed radiator valves, which prevents heat from being carried away. Because the heat cannot escape, the boiler shuts down to protect its internal components from overheating.
This fault is more common in autumn when heating systems are switched back on after being idle all summer, which can cause pump seizing or debris to shift and create blockages.
DIY fix possible
Check that the main isolation valves underneath the boiler are fully openEnsure at least two or three radiators have their valves turned to the maximum settingCheck that the boiler pressure is between 1.0 and 1.5 bar on the gauge
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