Thanks for the all the responses so far. To explain to you all further ...The original installation was made during an extension to an existing house. The area in question is roughly 5M sq. or 57ft. sq so a time clock operated 500 W underfloor heating element should have been ample. The bathroom is properly insulated and there are no drafts or such. I personally watched the installation which was carried out according to the manufacturers specifications. Laid on a floor base of concrete and encased with the appropriate insulator/grout/sealer, then over laid with ordinary thickness ceramic tiles. This contractor has never had a failure like this before. I and my Electrician colleagues cannot understand why it will not heat up as compared to other identical installations which reach a nice 27C.+ within the hour and operate on a time clock. The current draw is 2.1A at 230V. ac. I have tried out a 30V. 'Boost' giving a 2.6A draw. Which resulted in only a 1C. rise over an hour, so as most of you have suggested, I think it looks like a base board heater to supplement unless anyone else can see a way around this I certainly do not want to tear it all up and replace, all though the contractor has agreed to do so. For the sake of a trial I am borrowing a 55V. transformer just to see what will happen although as several of you have said 500W = 500 W !
Trumpy , you can see how I do the voltage boost, see "Buck/Boost/choke test drawings" by 'Scott35' in the technical area.
