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Thermostat well

I replaced a thermostat well on 4 inch copper domestic hot water line just 14 months ago, It was a pure brass Winters well, the original was a Weiss that failed in the same way but had been in place for years and was only noticed when thermostat was getting replaced. The well both times has looked like this,, any thoughts on what may cause this so quickly?


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,688
    What are you measuring the temperature of? Sulfuric Acid?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Dathis
    Dathis Member Posts: 6

    What are you measuring the temperature of? Sulfuric Acid?

    City water in Alexandria Virginia, I'm considering bottling it as an etching compound
  • pecmsg
    pecmsg Member Posts: 4,381
    They do make them in Stainless Steel. 

    Crap Brass or water issues. City water, contact them and ask them what’s up?
  • BenDplumber
    BenDplumber Member Posts: 48
    Softened water with a pumped DHW return? Appears to be dezincification. Are these these wells LF brass? I would check the grains per gallon of hardness, had two hospitals with the same problems with t-stat wells and thermostatic mixing valves. Ended up being the water softening contractor increased the pounds per regeneration on the control so they could sell/ deliver more salt. Once decreased to where the grains per gallon was around 3-4 the maintenance nightmares went away. Copper Development Association can be a source of useful information as well. Hope this helps you find a solution to the problem
    DathisLarry Weingarten
  • Dathis
    Dathis Member Posts: 6

    Softened water with a pumped DHW return? Appears to be dezincification. Are these these wells LF brass?

    Yes they are Lead Free brass, I hadn't thought about dezincification, there is no water softener system, but the city water does tend to run closer to 8 on the PH scale and the water temps average 140-150 both of which are known to accelerate dezincification, I will probably follow @pecmsg advice and have them invest in stainless steel thermowells going forward

  • hot_rod
    hot_rod Member Posts: 20,725
    The hotter the water the more aggressive, and more mineral precipitation .

    At some point a strap on temperature gauge makes more sense. I feel they are as or more accurate if insulated. Many precise controls use strap on thermistors, tekmar for one.

    With a well type you have to transfer through the well wall and through the wall of the probe. Assuming it was installed with transfer grease🥸
    With strap on pipe to thermistor is faster, less thermal lag.

    With that much sediment I suspect it wasn’t reading too accurately?

    Winters and others have digital strap on gauges.

    velocity can take them out, electrolysis also. That looks like hard water. Check the bottom of the water heaters for example if sediment make up.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Larry Weingarten
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,137
    Hi @Dathis , I agree with Hot Rod. There could be a degree of galvanic corrosion going on, with all the exposed copper chewing on the brass. Unless you can find a copper thermostat well, I like the idea of going with a strap on sensor. Stainless can be a little or a lot noble to copper, so the wrong stainless well could damage the copper.

    Yours, Larry