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brown spots in pex tube with matching defects on exterior of tube

My radiant system is driven by Combicore boiler/domestic hot h2o. In service for 6mo. of heating. Both supply lines (two) show rust colored internal discoloration and there is raised defects on the outside of the tube (photos) matching the area of discoloration. Surface defects are only in the discolored areas. Defects occur randomly along the entire length of the tube from the copper boiler connection to the manifold. Different brand of tube past the manifold shows no such anomalies on the supply side in the 3 feet below the manifold prior to going into the floor. No anomalies exist anywhere on the return side. System is filled with softened domestic well water with no other additives.

As the defects run sporadically the length of the supply tube. As such I find it hard to believe that physical damage to the o2 barrier from "fishing" the pex is the issue. Defects occur both on the end of the tube run that was pulled and the end nearest the spool at install.

I would welcome your perspective as I fear the possibility of splits or pinholes coming from this anomaly going forward as this is a 6 month old system.



  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    What brand of pex is it? I can't say that I've seen this before. Now when you connect pex to a wood boiler or something like that, it is normal for the inside to become discolored from the iron/rust deposits.

  • RobG
    RobG Member Posts: 1,850
    It appears that the rust spots are occurring where there is damage to the O2 barrier. As Harvey asked, what brand of pex is it?
  • Canucker
    Canucker Member Posts: 700
    I have the same spots in my tubing, combination of Heatlink and Hepex. Lots of cast iron in my system and no water treatment yet as I'm in the middle of renovations, so rads are in and out on a semi regular basis
    You can have it good, fast or cheap. Pick two
  • hedhntr65
    hedhntr65 Member Posts: 2
    Aquaheat tube. Uponor tube on the other side of the supply manifold shows on defects/discoloration? Surprised that reaction on the inside of the tube has physically changed the exterior of the tube. Worried that the raised nub on the exterior may lead to pinholes?
  • JeffM
    JeffM Member Posts: 174
    It's likely happening the other way around. The exterior damage spots are breaks in the oxygen barrier layer, which allows oxygen to diffuse inward through the pipe wall and lead to the discoloration on the inner surface.