My linea 24 Central Heating is working fine.

Hot Water is only giving luke warm, temp. is at 34 degrees. but when flow at tap is closed the temp shoots up to 90 deg. on boiler display.

I have checked:
The water pressure at mains
Motorised Valve

I have replaced:
domestic heat exchanger
thermister on main heat exchanger.
thermostat switch on main heat exchanger.
thermister near dhw heat exchanger.
non return valve on bottom right of dhw heat exchanger.
Also replaced the valve bobbin in diverter valve (bottom left, located behind motorised valve).
Also replaced the water pressure switch, But have not touched the adjustable plastic screw heads on this switch.

I have noticed that the 22mm pipe that connects to "Diverter Valve Manifold" (main brass housing at bottom left) is very hot indeed, But the Domestic Heat Exchanger (DHE) body is luke warm. And so is the Hot water outflow pipe. As soon as the tap is closed, the temp shoots up to 90 and the DHE begins to get hot to same temp as main feed pipe.

Many thanks for your help.