I had an interesting weekend...starting up my floor heat. I have a "subray" style floor heat, tubes sandwiched between the subfloor and the finish floor. (Engineered wood floor).
Before, during, and after installation I had 70 PSI of air in the system.....held rock steady.
Saturday I flooded the tubes and purged the air. No leaks. Sunday I cranked up the heat and the @#$*#ing thing leaked after a couple of hours. (The garage below does not have a ceiling yet,so I could inspect it. drip..drip..drip)
I proceeded to demo 25 sq.ft of Maple flooring, there really wasn't much water. When I pulled the last board out, I found the problem. I had put a staple square into the tube.
To repair, I cut slots into the subfloor, brought the ends below (joist area) and spliced it together. I had just enough "extra" maple to put it back together. This part was amazingly smooth, you would never know what happened.
Apparantly the staple made a great seal until the pipe heated up and expanded.
So my quesiton is: What good is a pressure test?