Hot water problem.

This is my problem:
The boiler heats the water ok. The supply and return to the hot water cylinder gets very hot.All three pipes from the 3 port diverter are very hot.The supply outlet pipefrom the top of the top of the hot water cylinder only gets warm to the touch.The coming out of the taps gets just above warm.The boiler is set to max.The tank does not have a tank stat but seems to have a temp probe (but i dont know if this is a legacy from an old immerssion system).Do you think yhat the coil could be split,the water runs clear for the minute that i run it should i run it for a while to check ?

Hope you can help.

Where are you measuring/feeling the cylinder return? Make sure it's at the cylinder because anywhere else could be getting hot by heat conduction along the pipe walls.

If you have a temperature probe, what is it connected to that operates the MZV?