ufh heating on 20+ hours a day

[mgrover]

As above. Ideally it'd be less.

This might be the wrong forum for the Q. But the system is actually working fine. the system is in the 15mm insulation boards above a tar subfloor.

Are my next steps to start getting cavity wall insulation etc etc?

 

[ShaunCorbs]

Sounds like the slab is not very well insulated

 

[mgrover]

are the 15mm insulation boards not enough? tbf this 20 hours plus in this -4 weather. it does tend to get better as the external temp is above freezing.