Can anyone please help me identify replacement mixing valve?

galaxydog · January 25

I have a cast iron hydronic radiant floor heating system built about 25 years ago. After speaking with two different heating techs, I believe my mixing valve needs to be replaced. I don't have the $2k+ to spare for the job, so I am looking at changing it out myself. I was told it's a 1 1/4 " size. I don't see mixing valves that look like mine online though. Where mine (no labeling) is large and extends in the x, y, and z axis, these one's online seem compact and extend in the x and y axis. Can anyone please help me understand what part I need to replace it with.

hot_rod · January 25

Heatway sold that valve as the AllTemp 2. It had an orange label on top. I'm not remembering the manufacturer. The smaller mix valves they offered were Hoffman.

The is somewhat similar to the Watts 170, perhaps an earlier version.

If it still controls? the o rings could be replaced. If the small heat motor "pill" inside is bad, you need to find an OEM part

Screenshot 2026-01-25 at 11.29.06 AM.png

hot_rod · January 25

I actually still have a cut away of that valve. Only 2 o-rings inside, both at the top nut and around the stem. The valve mechanism itself is brass on brass.

Looks like someone tried to scratch out the name Watts on the bottom cap 😲

Screenshot 2026-01-25 at 11.54.00 AM.png

Screenshot 2026-01-25 at 11.53.50 AM.png

galaxydog · February 18

Hello hot_rod,

I am sorry for the late reply. Life threw me a major curve ball.

Thank you so much for responding to my post. I really appreciate your time and efforts.

I haven't been able to find this exact part. I also have trouble finding a replacement part.

Could you please suggest anything that could work?

EdTheHeaterMan · February 18

This might work for you: https://www.supplyhouse.com/Caleffi-523178A-1-1-4-Sweat-High-Flow-Thermostatic-Mixing-Valve-7-6-CV-Lead-Free

there are less expensive mixing valves but they may not be adjustable to the temperature you need for Radiant floor heat. @hot_rod may have a better choice for you.

hot_rod · February 19

unfortunately I don’t know if any other with that connection orientation

I am almost certain that is a Watts N170 valve

It has been replaced with a LF model, lead free, and looks a bit different.

There were repair kits available for those legacy valves

A rebuild kit is a lot less $$. That is s pricey valve to replace with a like version

The Watts website shows part numbers and kits for discontinued products Find the repair kit # and check e bay a lot of old inventory ends up there.

galaxydog · February 21

Thank you @EdTheHeaterMan for the suggestion. Do you think the low Cv value 7.6 of that Caleffi valve would be appropriate given the high Cv value of my old valve being 21 (assuming my mixing valve is the one listed in @hot_rod's picture)

mattmia2 · February 21

depends on what your application is. the Cv should be about what the normal flow of the circuit is. if you use a 21 Cv valve where the flow is normally 7 gpm the control of the temp will usually be poor.

hot_rod · February 21

what size is the heating load in the valve? That is how you select the mix valve.

That valve regardless it is 17 or 21 Cv it is probably way oversized. Suited fir 200,000 btu/ hr load, or larger

galaxydog · February 25

Thank you @mattmia2 for the input.

Thank you @hot_rod for your help. 'what size is the heating load in the valve?' My answer I was able to generate with the help of ai is

“In winter all radiant zones run at once, and the mixing valve supplies the mixed header for the entire radiant system. I don’t have flow right now because circulation isn’t working properly, so I can’t measure delivered BTU. For sizing purposes though, using typical radiant design loads of ~15–30 BTU/hr/sqft for a 3,500 sqft house gives ~52,500–105,000 BTU/hr (mid ~70,000). With a typical radiant ΔT of ~10°F that implies ~10.5–21 GPM (mid ~14 GPM) through the mixing circuit. So the valve should be sized around that flow."

Some context of layout

Dunkirk Cast Iron Boiler → circulator → mixing valve → Taco 0011 circulator → 6 zones

galaxydog · February 28

To be clear, I used the ai to help me understand hot_rod's question and word an answer together based on relevant information about my house. To my understanding the question, 'what size is the heating load in the valve?' is actually kind of complicated and not very calculatable if your system is down.

mattmia2 · February 28

ideally you would have the design documents from when the system was designed, otherwise you would have to go off a combination of what you can see of how it is installed and heat loss calculations for the building to figure out what flow and temp is needed. even though you say radiant in like the first sentence i was thinking domestic hot water for some reason.

is it not maintaining temp or is it just leaking? if the packing is just leaking it might be easy to fox that. if it is stuck you might be able to disassemble and clean it instead of replacing it. if the element has ruptured or the seat has eroded then you have to replace at least the cartridge.

galaxydog · February 28

@mattmia2

Thank you for your comment.

'is it not maintaining temp or is it just leaking?' The boiler will run for 5 mins and then shutdown from overheat and then loop on and off. Water is hot on the incoming and cool on the outgoing of the mixing valve indicating some kind of blockage. It's weird because if I isolate the zones away and run home's cold water through the mixing valve it flows through and out into a bucket. The first tech was perplexed by this.

'if it is stuck you might be able to disassemble and clean it instead of replacing it.' The hex on the front doesn't unscrew off the front. It just spins left and right a bunch of times for adjustment I suppose. I guess I can cut the valve out and try to clean it with q-tips and brushes?

'if the element has ruptured or the seat has eroded then you have to replace at least the cartridge. 'After cutting it off I suppose I can replace a cartridge? I can't find a reference to this mixing valve online besides what hot_rod found so not sure where to get parts.

hot_rod · February 28

This is the repair kit, it has been discontinued, you may find one somewhere. start search for that part number.

The other option is to replace it but that will take some repiping.

Any thermostatic valve with a 7- 10 CV should work.

Can anyone please help me identify replacement mixing valve?

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