Your boiler has shut itself down for safety because a internal limit was exceeded, likely due to overheating or a lack of water circulation.

NTC1 short-circuited (NTC1 = outlet sensor) Probe manifold short-circuited

What causes this fault?

This fault occurs when the boiler's internal temperature rises too quickly or exceeds a safe limit, causing the system to shut down to prevent damage. The most common reasons are a pump failure that stops water from moving or a buildup of debris and sludge that creates a blockage within the heat exchanger. This lack of circulation means the heat produced by the burner has nowhere to go, triggering the safety sensors.