How to clean a thermostatic mixing valve?
May 28, 2015

How do I clean a thermostatic mixing valve?

Domestic water applications, particularly in North America, are challenging because our water can be very hard (have a high mineral content) compared to Europe.  Our colleagues across the water remind us of this regularly!  Fortunately, the 521 and 5231 Series mixing valves are designed to stand up to our tough water conditions!

Caleffi 521 Series and 5231 Series TMVs are high quality, high performance valves that can be used in either hydronic or plumbing applications. Because most of the valve is made of low lead brass, they meet the Reduction of Lead in Drinking Water Act, are ASSE and CSA approved, and are very popular for use in plumbing applications across North America.

Whenever hard water is heated, limescale deposits form which can have an adverse effect on moving parts and piping in general. That, and other forms of dirt and corrosion, can cause any mixing valve performance to suffer if allowed to get out of hand. The good news is our valves can easily be cleaned.

Watch this short video, featuring Cody Mack; he will explain how to maintain your mixing valve to keep it working great!

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John jesse
February 12, 2020

What is the expected life of your mixing valve in an area with high water quality? We got less than 2 years - the problem seems to be the o-rings - they have turned to goo
When this happens is the valve considered disposable?
I have the idea that new o- rings would fix the problem, is that incorrect?

February 12, 2020

Hello John, Water quality affects every product differntly and there are a numeber of ways to evaluate water quality ie.. hardness, PH levels, Clorine as well as other chemicals or metals in the water and the percentages that are present and how they react with each other. With that said if you are having issues with a product i would direct you to email photos to our tech support line. and we would be happy to help you work through this. Photos are always helpfull to determine if this is a water qualty or product issue. Thank you, Dan Firkus Caleffi North America

August 09, 2022

Hi there, seems like my thermostatic valve has stopped working and I'm not quite sure I am able to remove this to clean it. The valve is not mixing hot and cold water properly and I'm only getting cold water come out of my shower. Will I need to replace the entire shower?



In reply to by Mazen

August 10, 2022

Thank you for the photo. That appears to be the shower mixer, not a Caleffi 3-way mixing valve. You may want to contact Caleffi tech support @ 414-238-2360 to discuss.

Raja Sait
January 06, 2023

What is part number for 3/4" inch Thermostatic Mixing valve seals (green O-rings) and how many of them to be repalced as part of cleaning the mixing valve with vinegar solution.


In reply to by Raja Sait

March 21, 2023

Raja, regardless of tailpiece size (1/2" - 1") or connection type for our 521 mixing valve series, the replacement washer part number is R20011. You will need to replace 3 of them, at the connections of the hot and cold inlet and the mixed outlet.