BoilerFaultCodesYour boiler has encountered an internal electronic error that is preventing it from starting the burner to provide heat or hot water.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The burner doesn't ignite, the fault symbol 'U' is displayed and 'Reset' flashes red / Control fault.
What causes this fault?
This fault occurs when the boiler's internal computer suffers a communication failure or an electronic hardware glitch. It is typically caused by a malfunctioning main circuit board that can no longer safely control the ignition process, or a wiring issue that prevents the control box from sending signals to the burner.
DIY fix possible
Locate the 'Reset' button or control on the front panel.Press and hold the reset button for at least 2 seconds while it is flashing red.Wait for the boiler to attempt a restart; if the code persists, a professional must inspect the internal controls.
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A boiler cover plan would cover faults like U — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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