I too once lived in a house with them and they were fine.
It could be that the elements in the heaters are not all heating up because they are knackered or connections aren't brilliant.
Is it a constant temp all over or are parts hot and parts not so hot?
If there is a diffrence it's...
some of the floor tiles in my house, 4 years old and Barratt quality(!) appear to be rocking and some of the grouting is cracking.
Have I got a big problem or is it a bodge job which can be fixed by a tiler taking them up and re laying?