I mainly use cooper but behind kitchen units and in tight spots in lofts I will uses plastic, sometimes use the fittings with cooper were you can't solder.
Phone wb they will come out as it should be under warranty if not you can just phone them yourself and warranty it. Check it has been flushed first because if the gas is alright thats the next thing to be checked. I have numbers if you have not being left paperwork.
I think you do need a link I think it is ls, lr. The tr2 cable may not be correct I think it should be run in cat 5 cable as it is classed as data cable, this stops voltage from other cables affecting the tr2 or it could just be busted.
My boilers in the loft old cdi been up there 3 years never had a problem, install lots of boilers in lofts often the only suitable place in terraced houses. I thought the requirement for a handrail had been dropped