Mixing valve for radiant - how does it work?

sanjayp

I was testing my system heating after a recent install of an indirect. The boiler ran up to 180 (which I think is a problem in itself since it is 80 degrees outside and I have a modcon)... putting that aside as I try to reach the designer who programmed it, I noticed that temp gauge going into the radiant manifold was also running at 180. The mixing valve preceding the pump doesn't seem to be doing anything. This past winter, it definitely worked and I would see it running 20degrees or more lower than the boiler temp (higher needed for my radiators).

How is the mixing valve configured? It looks like a mechanical part. So what controls the temperature? I see a red cap on the bottom (see picture) ... if I turn it it simply goes around and around. The part is less than a year old. How can i tell if the mixing valve is working? Or can someone tell me how you configure it?

sanjayp

OK. Read up a little. I believe it works just by mixing the return water with the supply water.. so there's no magic here other than mixing hot water with colder water. The return temp is reading 140 degrees and I can feel that side of the valve is warm but colder by than the supply side. So the valve doesn't seem to be doing anything if 180 degrees is going into the manifold. how can i be sure it's mixing?

ratio

What's the temperature of the water coming out of the mixing valve?

hot_rod

You have it correct, it opens and closes ports on the H&C side, based on temperature. You need at least a 20° temperature difference between the hot supply and mixed outlet for them to perform accurately. Sounds like you have that.

Are there isolation valves around the valve?

Here is a cutaway view, as one port open the opposite one closes.

I would disassemble the valve, carefully as there is a spring in there, clean or replace the cartridge and o rings, or replace the entire valve. Occasionally the thermal "pill" in the bottom fails.





Notice the condition of the water that you drain out, usually bad fluid conditions are the cause of sticking or failed valves, you may need to run a cleaner, flush and refill the system fill with good clean water.

Zman

It seems likely that the addition of the indirect has something to do with this. A picture or schematic of you piping would help.

Solid_Fuel_Man

How were you heating your DHW before the addition of the indirect?

kcopp

he has a TT Challenger boiler w/ a coil built in. He abandoned it for the indirect.
Did he go into the control to change the set up so that the boiler knows its a cold start boiler vs. a tankless.?
Furthermore there are 2 sets of dry contacts for the heat and hot water.
If the outdoor rest was used you should not be able to run the heat if its 80F outside.
Something is not right.....

sanjayp

Thanks for the guidance. Kcopp must be right that the ODR must be disabled because it's 80+ outside. The mixing valve issue I think is something else. I'm going to run it be the plumber when he's back from vacation. The mixing valve should be independent of the ODR.

hotrod - thanks for the details. Gives me some background to speak to the plumber.

kcopp

Here is the control manual.
Page 56 starts the adjustments.
Pretty easy to make adjustments.
However if he mis-wired it that is a bit more of a chore to fix.

http://s3.supplyhouse.com/product_files/Challenger Combi Manual -Install2.pdf