I have a pipe which is leaking very slightly on a solder joint 8mm above my laminate, the pipe goes into a solid concrete floor and there is no way to drain down to that level, I have tried one of the special silicons and it worked for a while.
If the leak is on your heating system then try an internal leal sealer (bit like using radweld in the car) Fernox and Sentinal both produce internal leak sealers for heating systems, can either be pored into the f&e tank or injected into a radiator via the air vent plug.
Martin
November 2008
they make special fittings that snap into place a little pricey but work well
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Try fixfault.com to fix home heating systems.