Most UFH systems for upstairs wooden floors use a metal spreader plate with the pipe located in a preformed channel in the middle and fitted immediately under, and in contact with, the floor!
In my view your system is not suitable for the job and clearly fitted by someone who has no experience of UFH at all.
Tony
^^^^^This
The system shown is called "pipe and staples" where the pipe is fixed directly to the Insulation board, and a screed is then applied over the top, mainly used on ground floors due to construction methods and weight issues.
The way it has been installed is most inefficient, heating all the void before some heat may find its way into the room above. No wonder your bills are so high.
As Aglie says ' to work well, it should be made up as follows,
noggins set along the joist at the correct depth for the insulation board to sit in.
Aluminium spreader plates with a channel for the pipe to sit in.
When the floor is fitted, this should be in contact with the spreader plates so that the heat from the pipe transfers to the spreader plates and in turn to the floor.
The system you have got, in my opinion, is not correct for the application it is being used in.
It has either been done by someone who doesn't know what they are doing or the builder has done it as cheap as possible
