Q: What causes white and green buildup on plumbing valves?
A: That buildup is typically mineral deposits and oxidation. The white residue is often calcium or lime from small leaks or moisture escaping around fittings. The greenish color indicates copper oxidation — a normal reaction when copper or brass is exposed to moisture and oxygen over time.
Because it’s showing up mainly on the recirculation loop, the heat and constant water movement likely speed up oxidation. The circulation pump and fittings may also have minor seepage or sweating that allows minerals to build up as the water evaporates.
Q: Why is it worse on the recirculation loop?
A: The loop keeps hot water flowing constantly through those lines. That steady heat accelerates both mineral precipitation and galvanic corrosion — especially at brass or copper joints. Bathrooms or sinks not connected to the loop don’t experience this because the water cools between uses.
Q: Could the water softener be part of the problem?
A: Possibly. While a softener reduces scale, softened water can be slightly more aggressive to metal over long periods. It can cause fittings to corrode faster, especially if the system isn’t balanced or if the pH is low. Have your water tested for pH and hardness to make sure the softener is working correctly.
Q: Should I unplug the recirculation pump?
A: If you see moisture or active dripping, unplug the pump until a plumber can inspect it. If it’s just surface buildup with no leaks, it’s safe to leave running. Clean the fittings with a mix of vinegar and water to remove surface deposits, and check back in a few days to see if moisture returns.
Q: What should a plumber check?
A: Have a licensed plumber inspect the following:
- Any leaks or sweating fittings on the recirculation loop.
- Condition of the check valve and pump seals.
- Dielectric unions between copper and steel fittings to prevent galvanic corrosion.
- Your water softener’s output and pH levels.
Once any leaks are repaired, the plumber can apply a corrosion inhibitor or replace badly oxidized fittings if needed.
I’m Chris Mayer , writing for Plumbing 101.