DIY - Thermostatic Mixing Valve Rebuild Tricks - Do this before you call a plumber!

No hot water? It doesn't get hot enough or last more than a few seconds? The (hot) tube out of your water tank feels burning hot to the touch, but the (main out) tube is either cold or cooler? Your mixing (thermostatic) valve is likely the issue, as it's allowing too much cold water into the main water mixture.
This is our second rebuild of the watts thermostatic mixing valve (a poor design really). Check our first video for complete, disassembly, cleaning and rebuild. This time around we discovered a few new issues (a few years have passed since last video).
Remember to make sure you clean all parts (in a vinegar bath). Use these tricks and start enjoying hot water again.
O Ring Sizes Used:
Main body Spinner (22x2mm)
One way valve - outer (17X2.5mm)
One way valve - inner spinner (9X2mm) - 10X2 fit as well but seemed to stick a bit).

[@NMranchhand]

Thanks for the view into this problem. The details you explained, I think, could make all the difference in seeing what’s going wrong. Well done.

[@coolfool32]

Thank you for showing this. I now have the confidence to take mine apart. At least, I think I do.....🙂

[@markybecker]

Thanks for doing this video. We are looking for a re-build kit too but the valve was discontinued sometime ago by Watts. I will let you know how we proceed with our repair.

[@yuriymarchenko9267]

Can you just block the cold side of the valve with a piece of plastic or metal?

[@lesdell]

Quarters work nicely!

[@JB-yh3xr]

The o rings you have on the outside are the wrong ones. The check valve is actually supposed to sit inside and be flush, the thickness of the o ring you have is incorrect and should be much smaller.

[@fast-wheels]

It's always a good rule of thumb to match o-rings according to the original (although sometimes they thin out over time). I did play around with a few sizes as demonstrated in the video... and I'm glad to report that the mixing valve has worked well for over a year since this rebuild (so I can attest to this).

[@KBradAdams]

what would happen if you left all the insides out would it work? Any danger of it damaging pipes? I don't care about it mixing the hot and cold, I want to control that myself!

[@fast-wheels]

if you left the insides out, it would just mix hot water with the cold... without any way to adjust, so it wouldn't work :(

[@KBradAdams]

@@fast-wheels What do you mean it wouldn't work? Would water not come out? Would water not still mix inside and come out? I ended up trying mine around like a plumber suggested and only cold water went to the tub. I actually purchased a brand new mixing valve put it on and adjusted and my water is still luke warm. I am so pissed. I am going to try to find a plumber that will by pass this POS completely. Brand new house with a soaking tub that gets luke warm?

[@fast-wheels]

@@KBradAdams That's weird. with everything connected, if you feel the pipes before entering the mixing valve you should feel hot in one side (CAUTION HOT) and the another pipe cold. If that's the case the issue will then will be your new mixing valve (likely a faulty unit, or it's not adjusted properly - but I'm leaning to the 1st case). What I meant by "it won't work" is by "removing the insides", it would just mix hot and cold water w/out any way to control it- so you would end up with a lukewarm mixture.

[@KBradAdams]

@@fast-wheels Oh That makes sense. Yeah both mixing valves produce the exact same temperatures when I adjust the top nut luke warm. I had 2 Plumbers who told me to reverse C to HOT and H to COLD or put the valve on backwards and it would bypass this but I did that and it did not work at all. I purchased a brand new valve and it does the exact same thing as the old one although this one is easier to adjust but still will not get passed luke warm water. I have another neighbor with the same issue, these are brand new town homes. The next thing I am going to do is try and adjust the red scald thing on the Faucet and see if it will allow me to adjust it at the faucet. I know there is an anti scald valve on that faucet but thought I had already turned it as high as it would go. Do you have any idea what would happen if I removed that red ring completely? Thanks again for the reply!

[@fast-wheels]

@@KBradAdams I can't see how just flipping the H to C would solve the problem... (unless the hot/cold bypass valve was stuck, but even then, not likely to solve the problem). Each mixing valve is different, so I'm not sure exactly how yours works. Other things to check include the water heater temperature setting, and at times, there are other anti-scald mixing vales in the shower/washrooms as well.

[@WiseOwl_1408]

Remove it. Life is better