Your boiler has switched itself off because it has reached an unsafe temperature and needs to cool down.

Safety temperature limiter by NTC activated. Flow-NTC not correctly thermal-connected or defective; appliance does not shut down

What causes this fault?

This fault occurs when the boiler's internal sensors detect that the water temperature has risen too quickly or exceeded a safe limit, triggering an emergency shutdown to prevent damage. The most common cause is a lack of water circulation, often due to a seized pump, a blockage in the pipework, or air trapped within the heat exchanger.