Does anyone know how to work this

[Leighd]

I’m at a loss here, underfloor heating in an apartment we moved into. If I turn on the switch on the fuse board it’s just on constant.

Can someone explain this and how to work it ?

 

[SJD]

This is a Divireg floor heating controller.

I've not found the instructions for the 750, but the 710 model is vaguely similar, and might be enough to understand it. Apparently they are far from intutive!

Edit: Just to add, there should not be a large hole to the right of the controller, looks like a missing blank, which needs fixing before someone puts their finger or something in it with possible risk of electric shock!