NitroPress
Member
(This seems to be the right forum - mods please move to General Plumbing if that's more appropriate.)
BACKGROUND
House is about 12 years old and has a combo hydronic boiler/tankless water heater. It uses a tempering valve that's been problematic since we moved in four years ago - water temp fluctuates from day to day and sometimes during use. I finally figured out the system and tried cycling the valve from min to max, tapping on it with a wrench, etc. and was able to get a decent and reasonably consistent temp out of it. (During this, the tip of the adjustment stem broke off and I had to use a small vicegrips to adjust it, and later JBwelded a new handle on. I wasn't rough, honest!)
PROBLEM
Last week, the temp plummeted to about 15 degrees over cold water temp and no amount of adjustment, banging, etc. would fix it. Since it's a Watts 70A, I took a chance on buying a whole new valve (because stores that carry just the repair kit aren't open on weekends, and I wanted to replace the busted stem as well). The valve is of course at the lowest point in three stories of plumbing, so I had to work fast, but I managed to replace the whole screw-in bonnet assembly.
NOW THE PROBLEM
I briefly got very hot water up the outflow pipe, then it cooled and now no amount of adjustment will get the temp past about 105F - from ~165-175F tank temp and 60F cold supply. The hottest output is somewhere in the middle of the adjustment - turning it hotter reduces the temp as much as turning it colder.
The old valve was fairly clean, just some surface patina. The water that came out of the valve on disassembly was lightly milky and then clear. I didn't have much chance to look into the valve body, but it looked clean other than surface patina. (We have conditioned and softened well water.)
What in the heck is going on with this valve? Why does an entire new core not produce normal adjustment range? Is it possible that the cold-water valve fixed in the body is messed up somehow? (I would have to drain all the hot lines to look, which would be a PITA as there are no floor drains in the basement, so I hope to avoid that.) If I pull the new assembly back out, what flaws should I look for or test for?
OTHER PROBLEM
It's completely secondary, but the valve is 1/2-inch and the cold inflow and hot outbound are 3/4 like the rest of the house. The valve is plumbed in with reducers from the 3/4. I am not sharp on this kind of tankless heater, but it seems to me like the installer used a half-inch because it was cheaper or he had it in the truck, and the valve should really be 3/4 to allow better hot water flow, which we could use. Is there a good reason a 1/2-inch valve might have been used? If this whole fix involves replacing the valve body, would it be worthwhile to do it with a 3/4? Or is there something about the balance of flow that necessitates the smaller valve? (I can post a pic of the installation if that would help.)
Long, I know, but I wanted to avoid days of back and forth questions... thanks for any insight or help!
BACKGROUND
House is about 12 years old and has a combo hydronic boiler/tankless water heater. It uses a tempering valve that's been problematic since we moved in four years ago - water temp fluctuates from day to day and sometimes during use. I finally figured out the system and tried cycling the valve from min to max, tapping on it with a wrench, etc. and was able to get a decent and reasonably consistent temp out of it. (During this, the tip of the adjustment stem broke off and I had to use a small vicegrips to adjust it, and later JBwelded a new handle on. I wasn't rough, honest!)
PROBLEM
Last week, the temp plummeted to about 15 degrees over cold water temp and no amount of adjustment, banging, etc. would fix it. Since it's a Watts 70A, I took a chance on buying a whole new valve (because stores that carry just the repair kit aren't open on weekends, and I wanted to replace the busted stem as well). The valve is of course at the lowest point in three stories of plumbing, so I had to work fast, but I managed to replace the whole screw-in bonnet assembly.
NOW THE PROBLEM
I briefly got very hot water up the outflow pipe, then it cooled and now no amount of adjustment will get the temp past about 105F - from ~165-175F tank temp and 60F cold supply. The hottest output is somewhere in the middle of the adjustment - turning it hotter reduces the temp as much as turning it colder.
The old valve was fairly clean, just some surface patina. The water that came out of the valve on disassembly was lightly milky and then clear. I didn't have much chance to look into the valve body, but it looked clean other than surface patina. (We have conditioned and softened well water.)
What in the heck is going on with this valve? Why does an entire new core not produce normal adjustment range? Is it possible that the cold-water valve fixed in the body is messed up somehow? (I would have to drain all the hot lines to look, which would be a PITA as there are no floor drains in the basement, so I hope to avoid that.) If I pull the new assembly back out, what flaws should I look for or test for?
OTHER PROBLEM
It's completely secondary, but the valve is 1/2-inch and the cold inflow and hot outbound are 3/4 like the rest of the house. The valve is plumbed in with reducers from the 3/4. I am not sharp on this kind of tankless heater, but it seems to me like the installer used a half-inch because it was cheaper or he had it in the truck, and the valve should really be 3/4 to allow better hot water flow, which we could use. Is there a good reason a 1/2-inch valve might have been used? If this whole fix involves replacing the valve body, would it be worthwhile to do it with a 3/4? Or is there something about the balance of flow that necessitates the smaller valve? (I can post a pic of the installation if that would help.)
Long, I know, but I wanted to avoid days of back and forth questions... thanks for any insight or help!
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