BoilerFaultCodesYour boiler has sensed that the water returning from your radiators is far too hot, causing the system to shut down to prevent damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Return Temperature > 80°C for 5s, the Slave board shuts down
What causes this fault?
This fault occurs when water is not moving through your heating system fast enough to carry heat away from the boiler, causing it to overheat instantly. The most common reasons are a failed internal pump that isn't pushing the water or a significant blockage within the boiler's heat exchanger. It can also be triggered by a faulty sensor that is incorrectly reporting a high temperature to the control board.
This issue is more common during the first cold spell of autumn when pumps that have been sitting idle all summer tend to seize up.
DIY fix possible
Ensure at least two radiators are fully turned on and not restricted by thermostatic valvesCheck that the internal pump is audible and runningInspect the system pressure gauge and top up to 1.5 bar if it is low
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