Hi! My central heating system is of the sealed pressurised type and I am losing about one bar of water pressure every three days. The plumber says it is probably a leak under the concrete floor and suggests using Radweld or similar to fix it. Can this be right? The pipework has been in place for nearly forty years and there has never been a problem before. The pressure relief valve and tank have been professionally checked and no problems found. Can anyone suggest how to locate an underfloor leak, there are obviously no visible suspect areas. Many thanks, David.

Grandadboilersuit, March 2010

Turn off water. Attach air compressor to water line listen for air bubbling into the lake under your slab. Do not overpressurize. You can pinpint the leak with a stethoscope or similar. Here there are specialty companies that charge around $500. to find and repair such a leak usually breaking only one 12 x 12 inch tile. the longer you wait the more likely you are to have catastophic slab damage.

max, December 2010

That is going to be difficult to find. The radweld idea might work and is worth trying.
Is there a way you can increase the pressure on the underfloor pipework? E.g. maybe connect a hand pump ( the type used for pressure testing pipework in new installations) to the system to increase the pressure above normal. What this will do is greatly increase the rate of leakage which may cause a damp patch to show at the surface.

JD, March 2010