Can I add check valves to your 521 Series Thermostatic Mixing Valves?
June 15, 2016

Can I add check valves to your 521 Series Thermostatic Mixing Valves?

Caleffi offers a wide selection of models with and without check valves for your convenience to compliment the 521 Series Thermostatic Mixing Valve family. Models with checks have a "...C" suffix, for example 521519AC.

If you have an existing model that does not have checks, for example 521519A and you need them, you will need to replace the "standard" tailpieces with new tailpieces that come with checks (see below).


These are a little longer than the standard tailpieces and have an internal machined groove that the check clips into. For a complete list of tailpiece choices, see the SMALL MIXING VALVE AND ZONE VALVE FITTINGS page in Section 9 of our List Price Catalog.

Don't order the plastic check insert (for example R39204) and try to install it in the "standard" tailpiece; it won't fit. The check inserts are made available for replacement purposes only.

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Blog post comments
Alex Salki
March 27, 2020

Can the Caleffi 252159A be used in an excess heat dissipation branch plumbed between/connecting input and output lines of a 2 panel EV thermal system ( total10KBTU/hr max)? The dissipator is capable of bleeding off 12K BTU/hr at flow rate 3 ft/sec at 180 F glycol/water input. Will cooling be sufficient to allow use of 252159A to combine dissipated fluid with hot (>180F) fluid from panel so that mixed stream is adequately cooled to protect thermal panels and storage tank by keeping system temps below 180F (80C)

March 31, 2020

Thank you for your question. The Caleffi 252159A is a thermostatic mixing valve that has a mixed outlet temperature adjustable from 80-150 degree F. The maximum inlet water temperature is 180 degree F and it is only ratered for use with water. The specificaitions do not inducate use with glycol. It requires a minimum 30 degree delta T between inlet water temperature and mixed outlet temp. I attached the technical brocure for you to review and you can contact Caleffi tech support anytime to discuss or email