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Thermostatic Mixing Valve Servicing

desert_sasquatch Member Posts: 118
edited January 16 in Domestic Hot Water
Future Homeowner (and non-expert!) here.

I'm watching Caleffi's "Hot Topics" show, and in episode 2 Bob Rohr talks about thermostatic mixing valves, and demos a DIY way to remove the scale from them by removing the valve from the assembly and pumping an acidic something through them until the scale has been removed (he mentioned vinegar and what I think was some kind of chemical descaler).

What I'm wondering is if there's a reason that he feels one needs to remove the valve in the first place ie would it be possible to put some kind of three-way valve between the shutoff valve (two way valve) and the thermostatic mixing valve, so that the vinegar could be pumped through the thermostatic mixing valve, to exit through the faucet and be returned to the bucket with the pump in it (if this sounds confusing see

Would the vinegar flush corrode or damage a faucet or PEX tube? Is the three-way valve thing just a waste of time and if so why? Am I focusing on the wrong aspect of thermostatic mixing valve longevity, and will these valves need replacing after 5-8 years even if I descale them regularly and manage the Langelier Index? For that matter, will valves that are used more--such as for the shower--require replacement sooner than valves used less, like for the bathroom sink?

I'm just trying to understand the maintenance implications of using thermostatic mixing valves just upstream of every faucet. If I have to replace all of them every 5-8 years it sounds like I could easily be paying a few hundred dollars a year for this in my not-huge (10 point of use valve) home. Whereas if I can prolong their life and make servicing them doable by a layman....that becomes a less expensive proposition.

Probably I just don't understand how all this is put together and there's a reason folks don't do this, but I figured I might as well ask, and hopefully learn something. Any information on servicing or the service life of thermostatic mixing valves would be welcome.



  • hot_rod
    hot_rod Member Posts: 20,790
    The service frequency depends on how much water flows through the valve and the hardness of the water. It is not so easy to predict when they start scaling to the point of not regulating properly 

    you could install a Webstone valve upstream of the central mixed and circulate a cleaner without removing. 

    Or Keep a spare valve to swap when they need a rebuild. Soak the removed one 

    Get rid of the scaling minerals by softening the water or add a phosphate doser to the water heater

    Some of the electronic mix valves have a self clean function. The LegioMix is a ball valve type and it rotates the ball every day to wipe scale off 

    No doubt the more valves you have in the system, the more work to maintain them.  At some point to o rings wear and it needs a new cartridge. The movement of the cartridge and the chemicals used in public water take a toll.

    Vinegar will not harm the valve or you.
    Even more powerful acids like Sizzle are approved for potable water treatment, also
    The ph of Coke us around 2.7, it cleans scale well👍🏻
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,475
    Those Webstone valves are The greatest invention. Love them!  Mad Dog
  • desert_sasquatch
    desert_sasquatch Member Posts: 118
    Hah wow, thanks Bob (and Mad Dog)!

    Maybe this is a question that misses important context, but how many times would you guess that you'd be able to descale a mixing valve before it craps out for other reasons? Or is that impossible to know because there are other factors at play here that are just much more important?

    Just trying to price this whole thing out.
  • hot_rod
    hot_rod Member Posts: 20,790
    There is really not a lot of parts to fail inside a mix valve. It’s very similar to a single handle shower valve. A plastic spool with 1/2 dozen o-rings

    On a shower valve you move the cartridge. On a mix valve a small copper heat capsule does the moving.

    Clean it on a regular basis, depending on the usage, and it will last longer Once it jams and you force it apart, more potential to damage the cartridge and o ring.

    You will have to determine the maintenance interval, no way for us to determine that. It could be every year, every 3 years, or every month.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream