Weird panels in wall of new house

[Pugliandreamer]

As the title says, our house is 1970s build (we've just moved in) and there are white wooden panels in most of the rooms (some behind radiators) which are a sort of trapeze shape and the size of a hand maybe. They seal an open area behind which we've found some black piping behind.
Does anyone have an idea what they are or what they're for? Our best guess is some kind of defunct heating system!

Are they an early version of a built in vacuuming system. A friend had one in a new house when I was a child. You could clean the room when people were sleeping. It was very futuristic then and had trapeze shaped openings.

If it is, there should be an emptying can somewhere all the pipes go to.