Ceramic Floor Tiles Have Dark Spots Over Heating Pipes

[greg]

Please Help!!

I have recently laid white ceramic tiles throughout my kitchen/diner about 4 months ago. I have laid the tiles on plywood using a flexible adhesive. Underneath the plywood is a concrete floor, which was put down in the 1970's.

However the problem is:- I have recently turned the heating on due to winter coming closer & the strip of white tiles which are directly above the heating pipes in concrete connected to the radiator have turned a shade of dark, almost as if they look damp underneath.

I have checked my boiler & it appears that pressure seems ok which to me would indicate their is not a leak in the pipe.

Any thoughts?????!!