Any heating engineers/ gas safe on here

[yogib5]

Need some advice please

My central heating is coming on, but we have no hot water,

A gas safe engineer has fitting a new honeywell 3 way valve but its still not heating the water up,

He doesn't know what else it can be

We have a system boiling, the one that's usually in a kitchen behind a kitchen unit, it's not a combi boiler

Its a icos he15, the boiler itself has just been serviced and the trap cleaned out

The grundfos alpha pump thats next to the copper tank has power and the lights to it are on

But still no hot water

Any idea