Bathroom Only Has Warm Water

[XenoMorph]

Hi all
So I live in flat with communal heating/hot water and so have a HIU in the flat.
I had a problem where nowhere in flat was getting hot water only warm and company that services the HIU came and replaced a valve in the HIU.
Then I was getting hot water in kitchen but not in the bathroom still.
One plumber sated he was puzzled as both shower which is a thermostatic mixer and the level mixer in basin had same issue.
Only thing he can think of is there must be a blender valve in the bathroom behind the tiles.
Is this reasonable? or could there be something else causing the problem?
Thanks

 

[Deleted member 120897]

Isolate the cold water entering the HIU, and run the hot tap, if it’s still running, I suggest that is your problem.