What could cause reoccurring leaks in a hot water pipe?
It depends on where the actual leaks are. If the leaks are at the solder joint, then this would indicate poor workmanship from the installer. If the pipes themselves are developing pinholes, then you could have gotten a bad batch of copper pipe that had impurities in it. Recycled copper used for pipes can have impurities in them which can lead to pinhole leaks. I have heard that this was a common problem for a while. I'm not sure if it has been resolved yet.