Ferroli 901 combi Intermittent/no hot water

I have changed the thermistor sensor on the hotwater supply and the flow sensor as the hotwater supply was intermittent. There is hot water now but it only if works if I connect an old thermistor to the wiring loom but not to the new one installed in the out flow to the hot taps. Obviously in this case it gets too hot. Any help please

This might sound illogical but try changing the CH thermistor.

Thanks. Fixed it by putting an old one back in. looks like the new one was US.