Central Heating works but no hot water? Worcester 28i RSF?

Hi I hope someone can help.

I have a Worcester 28i RSF Combi boiler that i have a problem with.

A few weeks ago i had a hot water leak from what looks like a flow switch at the front of the boiler (black in-line with arrow, 2 nuts, cable from the side) this was sorted by just tightening the top nut.

Around the same time the hot water temperature started to drop. It now does not heat the hot water at all, as if it doesnt call for the boiler to heat as i turn the tap on.

Central heating works fine, if the heating is on, i can sometimes get warm water in the tap.

Any ideas or similar experiences?