Communal Heating System - radiator and water not hot

[catflapuk]

Hello,

I live in apartment with communal heating system and have heat interface unit in my flat. From one day to another all radiators are not getting as hot was they used to and I have noticed the same with the water. I am clueless as to what the problem could be. Is it the HIU or the communal system that may have a fault? How can I find out?

Thanks