I am a homeowner who has a pressurized horizontal closed loop that loses pressure over time. My contractor used to have to add water to the loop every 4 to 5 months, just yesterday it was only a month since the last refill. When water is added, the contractor only needs to add a very small amount, approx. less than a quart to bring the loop back up to pressure. The contractor has searched everywhere inside the house where the loop is exposed and also inside the unit for leaks, but has been unable to find one. We are both of the opinion that the leak is somewhere underground. The loop is about 12 years old and began losing pressure about 5 years ago. The contractor has suggested installing a B & D non-pressurized flow center instead of digging to try to find the leak. Does anyone have any ideas on how one might find a pinhole size underground leak? Anyone ever try installing a B & D non-pressurized flow center on a leaking loop and how did it work out? I plan to be in this house for many years to come and want to fix the problem right and still have a cost effective fix. Two other suggestions he has had was plumbing in an autofill mechanism to the loop or using Geothermal Fix-a-Leak. I don't like the autofill mechanism because you never know what the mix ratio of methanol/water is and eventually the loop will become diluted with water. I don't like the Geothermal Fix-a-Leak solution because I believe it will hurt the efficiency of the system having slimy stuff coat everything inside the loop. My geothermal system is little undersized for the house to begin with and I need all the heat I can get out of it. I have also read about evacuating the loop and putting helium in it and then using a helium detector above the ground where the pipe are laid to find the leak. With the leak in the loop being so small, I am skeptical about whether this would work or not. It is said that helium is such a small atom that it will leak up to the surface of the ground and be detected. Any suggestions or advice you have on this matter would be much appreciated.