Hot water coming through cold water line
Hi, I recently had a water heater installed and am having a funny issue. We are periodically getting warm water coming through the faucets when only the cold water is turned on. I've read about cross connections, but I've determined that's not the case. In fact, I've determined that hot water is coming out of the water heater the wrong way, up the cold pipe, thus warming up the water. The expansion tank was installed on the hot side, so my guess is somehow this is providing sufficient pressure and volume of water to push it out the other side.
when this happens, if I leave the water on long enough then it will get cold again, but it takes a while and I don't want to waste all that water. I think he put the expansion tank on the hot side simply for ease of installation. He suggested not even putting it in, I think because he didn't have exactly what he needed. I think he would have had to move the shutoff valve on the cold side and my guess is he didn't want to do that either. He was saying something about not knowing it was 1/2" pipe, so I don't think he had a lot of 1/2" stuff. Anyway, it was replaced under a home warranty, and now I'm having a hard time reaching him so I thought I'd ask here to see what the best solution is. I have no plumbing skill when it comes to soldering copper pipe, so I'll have to hire someone if something needs to be done. Might the expansion tank pressure not be adjusted correctly? If so, that's something I could do. If not, what do you suggest? A check-valve? Moving the expansion tank to the cold side? Any thoughts and suggestions would be greatly appreciated. Also, I know you can't speak for going rates in Salt Lake, but any guesses as to what would be a reasonable cost to have a plumber come and apply whatever you suggest? Thanks in advance.