I found more cupric chloride on my pressure relief valve after back from a 2 weeks vacation, should I worry about it? And, what should I do before turn on the gas water heater?

It used to has some cupric chloride before, but not that much. It may already gain more cupric chloride but I didn't notice it before.


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  • All it takes is a little moisture and this will continue to happen until the pipe is cleaned and revarnished, I use plumbers abrasive cloth and a clear spray varnish. With the copper cleaned and sealed it will stay bright for years.
    – Ed Beal
    Dec 26, 2018 at 20:59
  • Hmmm, you need a 3/4" for 150 p.s.i. and 210°F to match your old one. The model should not really matter if the specs match and the probe is the same length (you will see the probe length when you remove the old one). Dec 27, 2018 at 23:45
  • the T&P valve is really tight, I'm not able to remove it. And, I saw some declaration above in the tank which I have attached the pic which said the relief valve is the combination of the water heater, does this mean I can't remove it? If no, how to remove a very tight valve? thanks @JimmyFix-it
    – Brian Z
    Dec 28, 2018 at 0:22
  • OK, that warning label is telling you that the valve is protecting the appliance from both over-heating and over-pressure (combination). The part about removal from point of installation is a warning that relocating it to another part of the system will not provide adequate protection (back in the day they sometimes located a pressure-relief valve on a pipe outside the home). You can remove and replace it. Pull off that plastic cover so you can see the threaded part. Get a bigger wrench, at the factory they use a pipe compound that sets hard. Your tank is iron and unlikely to be damaged. Dec 28, 2018 at 0:34

1 Answer 1


Wipe it off with a wet rag, then see if it comes back. This could be the result of too much flux being applied before soldering and the excess not wiped off. If you cannot get it off with water, you could try household vinegar on a rag, then wipe all the vinegar off with a wet rag.

The excess flux would have to have been carried down the pipe by water on the outside of the pipe. This could be water condensed from the air on a cold pipe or water from the water heater. If it's from the water heater you will probably find the source if you clean the pipe off and keep it under surveillance.

Where does your overflow pipe go--to the sanitary sewer or to the outside? You could see what happens if you open the PT relief valve by operating it manually with the lever. But only do this if it won't create a mess. Also don't run too much scalding water directly into the sanitary sewer because this might damage the drain piping.

EDIT There is no reason to delay getting the water heater back in service because of the deposits on the TP relief piping.

  • 1
    +1, I will add that excercising those valves by manually opening them can be a double-edged sword. It can help remove boiler deposits from the valve seat, assuring (hopefully) proper operation; it can also cause them to start leaking-by during normal operation. Dec 27, 2018 at 0:46
  • My T&P relief valve is keeping trickle after I manually flip the lever up, so I think I need replace it, one more question is can I use the "NCLX-5LX" to replace the "NCLX-5S" valve which is mine as I can't find the "5S" from home depot? @JimmyFix-it
    – Brian Z
    Dec 27, 2018 at 18:03

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