CORROSION ON HOT WATER SIDE ONLY?

[Gene South]

From todays inspection: Note the PEX manifold has oxidation on each of the metal fittings for each of the hot water branch lines, while the cold water blue PEX fittings do not have corrison. Oxidation only on the hot water lines. Still trying to sort this out but as to root cause. Anyone have an idea as to why oxidation on the hot side only?

[Dom D'Agostino]

Zurn has a spotty history with PEX fittings, including "dezincification" that causes corrosion and "stress corrosion cracking" that causes leaks and corrosion. Google it when you have time, there's plenty to read on Zurn and poor quality brass. Maybe there's a correlation to water temperature as well.

Dom.

[Benjamin Thompson]

Chemical reactions (including oxidation) speed up with heat. was there a water softener in the home?

[Gene South]

No water softner or any other water treatment. Just regular city water.

[David Bell]

Looking at the manifold, the top hot valve has no staining except at the connection to the manifold leading me to believe there was a leak the soaked the rest of the valves.

[Benjamin Thompson]

Looking at the manifold, the top hot valve has no staining except at the connection to the manifold leading me to believe there was a leak the soaked the rest of the valves.
Bet you're right on that!

[Kyle Smith]

(Long shot) Hydronic heating systems can cause corrosion from oxygen concentration but it's pretty much limited to closed loop systems with ferrous metal components and non-oxygen barrier pex.

[Rich Goeken]

From todays inspection: Note the PEX manifold has oxidation on each of the metal fittings for each of the hot water branch lines, while the cold water blue PEX fittings do not have corrison. Oxidation only on the hot water lines. Still trying to sort this out but as to root cause. Anyone have an idea as to why oxidation on the hot side only?

Gene, with reference to Kyle's comment "(Long shot) Hydronic heating systems can cause corrosion from oxygen concentration but it's pretty much limited to closed loop systems with ferrous metal components and non-oxygen barrier pex.," did you notice any deterioration of the hot water lines at the far end (sink, etc.if visible)?

[Michael Bronner]

Gosh, my guess is simply that the hot water lines are condensing moisture when trapped inside this wall cavity and is probably only occurring during certain months. It looks like it's in a basement and the foundation wall is close by, there is no moisture barrier on the foundation wall, no insulation nearby and perhaps it's just condensation on the hot side...I would not lose any sleep over this one unless it is condensing moisture enough to drip onto the floor and framing below and cause staining on the finished material.

[Benjamin Thompson]

Gosh, my guess is simply that the hot water lines are condensing moisture when trapped inside this wall cavity and is probably only occurring during certain months. It looks like it's in a basement and the foundation wall is close by, there is no moisture barrier on the foundation wall, no insulation nearby and perhaps it's just condensation on the hot side...I would not lose any sleep over this one unless it is condensing moisture enough to drip onto the floor and framing below and cause staining on the finished material.
You need to think about that answer:)

[Tom Rees]

Gene, Did you notice if the hot water from tap had a smell to it. I ask because I think Benjamin was on to something with his oxidation theory. I know we all just guess but that is one of the fun parts of this forum. It's interesting to hear all the different theories. It gets your mind going.:D

[Rod Corwin]

I noticed each of the nuts on the handles are progressively rustier from top to bottom. When those lines are cold condensation builds on them during humid months. Top valve deals with its own condensation. His lower neighbor deals with his own and his buddy above. The one on the bottom gets 8 neighbors dripping on him. So each is progressively wetter. Add heat increase oxidation increased moisture worse at bottom than top. That in combination with poor quality brass as previously stated is whats causing this. Just a hypothesis.

[Gene South]

Guys, the manifold is not in a basement and this is a dry environment (Texas). We generally don't have humidity build up or condensation on water lines, and there did not appear to be any leak. My guess the hot water has speeded up the dezincification process. See the first response by Dom and research PEX fitting issues with dezincification. My guess that is the issue.

[H.G. Watson, Sr.]

Guys, the manifold is not in a basement and this is a dry environment (Texas). We generally don't have humidity build up or condensation on water lines, and there did not appear to be any leak. My guess the hot water has speeded up the dezincification process. See the first response by Dom and research PEX fitting issues with dezincification. My guess that is the issue.

#1 Suspect the "guest bathroom" doesn't get a lot of use, especially enough to regularly flush the HOT water line - stagnant water after having traveled through WH concentrated agressive 02 issues - plumbing dead end. Cold valve pictured dirty finger marks - possibly replaced already by plumber who didn't wipe hands. :D

Storage type water heater? How old? If so, pull the anode and inspect, likely time to replace it. Zinc sacraficing. What's the water quality?
Also as mentioned - stressors when no demand cools, when demand hot water running through heats up, when not used...cools down again. Treated (chlorine residuals, concentrated minerals, etc.) heated water more aggressive. Bad (brass mix wrong) valves and wrong handles/nuts.

[Vern Heiler]

Looks more like the type of corrosion found on battery terminals. Is the water heater electric? Did you test for voltage? Could be a leaking element.

[Gene South]

Hello H.G. and Vern. Good input from both of you, thanks. The water heater was natural gas and 7 years old if I recall. I think H.G. is getting close to figuring it out. Water is hard water with high minerals. All those things likely figure in. Anyway, thanks again.

Gene

[Stephen G]

I dont think the fittings are the same material on both side. So it might be galvanic welding (shock), or disimiliar metal welding.
The parts on the left are reacting badly and creating premature oxidization and the nut is acting like a anode and taking the hit for the team.
Scrape up that hot fitting and see if its brass or white metal.