Copper failing under the house

Question

I am in a 10 year old house. Custom built, very nice home. Twice in the last year, have encountered a leak under the slab.

History

• The first time about a year ago, I agreed to have the lines rerouted overhead in attic with PEX. Worked fine.
• This month, another leak happened in the other end of the house, again, the hot water side.

The House

• The house was on a circulating pump that ran 24/7.
• We are on hard water that has a high pH factor out of the tap.

The Plan

• I am going to have the entire house re-routed with PEX in the attic.
• We are in a fairly cold climate (Oklahoma) but the attic is well insulated and we are going to have them insulate the pex.
• I don't want to jack hammer up the floor every six months because it is an expensive wood floor, and tile in some areas.

Here's my question(s):

1. Would the running water from the pump create more friction in the copper pipes thus creating a breakdown in the copper?
2. Should I just re-route the HOT Water? The cold water line has yet to fail, and I would have to tear out some tiled shower walls where the outdoor faucets are, and prefer not to have to rebuild the showers, however, if the cold water is intent on failing soon, might as well replace both at the same time.

Answer 1

when conduit or plumbing is covered in concrete it must be insulated from the cements high alkalinity, otherwise the metal will corrode and eventually fail. I don't believe the circulating pump has any detrimental effect on your copper pipe. Although it should be on a thermostat so it only works when needed. What I've noticed alot more in recent years is the quality of copper pipe (most imported from overseas) has become much lower. This and a high pH level could be why the copper is failing. If you are going to replace any damaged pipes it would be wise to re-route the pipes in the concrete to be safe. PEX when installed properly is the better alternative than copper.

Answer 2

Depending on the makeup of the concrete, e.g. if fly ash is used, there can be a chemical reaction that degrades the copper. That said, 10 years is awfully fast for copper to fail in concrete. Perhaps there's been frost damage, or some other cause. The only other theory that comes to mind is the recirculation pump could have caused an static electric charge buildup that accelerated any chemical reaction, but that's honestly a wild guess. As others have hinted, get a good look at the pipe and have an expert determine why it's failing if you want to know for sure.

Regardless, PEX run from above is a much better option for maintainability. To minimize the freezing risk in cold climates, run the insulation over top of the pipes, forming a "tent" of warmer air around the pipe. If possible, don't have any insulation between the pipe and ceiling to maximize the warmth from the home. That's the advice that was given to me on a project that had sprinkler lines (apartment building) running through the attic. Even if it were to freeze in the attic, without any joints, the PEX is unlikely to burst.

This is getting into an opinion, but if it was my home, I'd convert all the water lines, and not just the hot lines. It's more work now, but less work than doing two separate jobs should the cold fail later, and it means all future work would only need to deal with one type of pipe instead of mixing and matching parts and tools for different systems.

Answer 3

A continuously running circulation pump along with high mineral content water, if combined with cheap thin walled copper pipe (Type-M, look for red manufacturing stamp) and poor installation technique (failure to ensure smooth flow by reaming/deburring pipe) could very well lead to internal erosion failure in 10 years.

Whether or not you reroute everything or just the hot water (your post says"I am going to have the entire house re-routed", which makes part of your question confusing), you need to install a thermostat on your pump so it only runs when needed. You should also install a switch to shut the pump down whenever you are away for a significant amount of time.

If investigation reveals shoddy materials and/or workmanship, you should definitely replace the cold water side as well.