BoilerFaultCodesYour boiler has stopped running because it senses that even though the burner is lit, the water inside isn't getting any warmer.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: No primary temperature increase detected
What causes this fault?
This fault occurs when the boiler fires up but the sensors do not detect a sufficient rise in water temperature, causing the system to shut down for safety. The most common reason is that the water isn't moving through the unit properly, often due to a failed internal pump or a blockage in the pipework. It can also signify that the sensors responsible for measuring heat are faulty or that the main heat exchanger is clogged with debris.
This issue often surfaces during the first few cold days of autumn when heating systems are turned back on after being idle all summer, which can cause internal pumps to seize.
DIY fix possible
Check that the radiator valves and the main isolation valves under the boiler are fully open.Ensure your system pressure is topped up to between 1 and 1.5 bar.Try resetting the boiler to see if the error was caused by a temporary air lock.
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