Every two weeks I'm having to bleed the central heating system does this meen it is leaking if so how do I go about tracing were the leak is. There is no visible leek unless it is in the concrete floor can anyone help

It is a good possibility the leak is in the floor. There are untrasonic meters to test for slow leaks. A plumber in your area might have one.

It is very difficult to tell exactly what your problem is with no visible leak. This is why whenever I hear about pipes in concrete that is the first location to look. The chemicals in concrete do not like pipe some type of pipe more than others.