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.

[coolfool]

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

[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.

[BugzKiller]

The one that came with the furnace is 11 years old and it just started leaking like crazy at the valve where you turn. Funny thing is I never touched it. I just ordered a same model one off the internet from my plumbing supply Warehouse.

[keizomatsuzaki]

Mine has a thermostat on the hot water tank. Why do I need a mixing valve to control temp.?

[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!

[yuriymarchenko]

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

[JB-yhxr]

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.

[davemaccammon]

🎉just saw this. Is this for a WATTS LFMMVM1-UT the EDP #0559119.