Multiple tempering valves don't work

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Chesterton

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Well, this one has me stumped:

We have a tankless water heater that also supplies a heat exchanger inside for "emergency heat" when our heat pump needs help. The water heater provides water at 160 degrees, which I have confirmed. It goes to a tempering valve before it supplies the rest of the house. Originally the water post-valve was 120 degrees. Several years ago it dropped to around 99 degrees, even with the valve at max temp. I finally got frustrated with luke-warm showers and, figuring that the valve (an Apollo TV 34-200) had gone bad, I tried to rebuild it. The water was still 99 degrees. So I replaced the entire valve with a Honeywell AM-101 and.....water temperature is still 99 degrees. Like with the Apollo valve I can adjust it down colder, but the max is 99 degrees.

Since thermostatic valves are also pressure sensitive I'm wondering if there could be a weird pressure imbalance in the system? I'm wide open to suggestions here.

Thanks!
 

Chesterton

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This is the best I can get. There's not a lot of room in there. I can diagram it for you if that would help. I tried to align the two pictures, but I'm sure you get the idea. Note that there are a bunch of one-way valves in there.

Like I said, it worked reasonably well for a number of years before it had a problem. I wondered about the expansion tank. It seems to be working--currently at 72psi.

plumbing.jpg
IMG_7099.jpeg
 
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Chesterton

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I should add that at the valve the hot is 150 degrees and the cold is 49 degrees. It leaves the valve at 99 degrees. I can change the temperature at the tank anywhere from 120 to 185 and the mixed temp is within a degree or two of 99.
 

Reach4

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The water heater provides water at 160 degrees, which I have confirmed. It goes to a tempering valve before it supplies the rest of the house. Originally the water post-valve was 120 degrees. Several years ago it dropped to around 99 degrees, even with the valve at max temp. I finally got frustrated with luke-warm showers and, figuring that the valve (an Apollo TV 34-200) had gone bad, I tried to rebuild it.
Can you measure the temperature on the pipe that is feeding the input hot water to the mixing valve? I presume you have an IR thermometer.
 

Chesterton

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To begin with a tankless water heater doesn't need an expansion tank.
At first I thought that was left over from the previous system and that maybe I could pull it. But there is a closed, recirculating loop in the system that feeds the emergency heat at the heat pump. There is no storage fixture there, but would that necessitate the expansion tank?
 

John Gayewski

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Your tankless isn't piped for recirculation correctly from what I can tell.

Usually if something works for a time and then stops you either changed something or something broke. Generally a check valve is stuck open or broke or someone hooked the hot and cold together with hoses.

Code is gonna require an expansion tank weather you have a tankless heater or not. They make tiny ones for tankless heaters now.
 

Chesterton

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OK. I apologize for the delay--big day at work yesterday. I have created a diagram of the system since the pictures sucked. It includes everything that I have tested in the system. I agree with John that if something worked and now doesn't that something changed. I assumed first that the heater, then the mixing valve were the culprits but was wrong on both accounts.

plumbingDiagram.jpg
 

Fitter30

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First the check left of the water heater and pump isn't needed. These valves can't have have any more than 30 lbs difference between hot and cold. When was the heat exchanger cleaned? Brand and complete model number of heater? Hows the emergency heat work?
 

Chesterton

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Heater cleaned annually and completely overhauled two weeks ago. Rinnai 94LSi propane with the commercial controller (to enable higher temp settings).

Emergency heat gets called by the thermostat at temps near freezing. Turns on the pump which sends hot water to the heat exchanger inside the blower, comes back cold. I have not cleaned the heat exchanger. It hasn’t been active lately so I haven’t put the gun on it for temps in and out.
 
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James Henry

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Your drawing probably is right, it's just me. The bottom line is that if you have 150 right up to the mixing valve then what else could it be then the mixing valve. It doesn't matter that it's brand new. If you don't have 150 up to the valve then you have to trace it back.
 

Chesterton

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Your drawing probably is right, it's just me. The bottom line is that if you have 150 right up to the mixing valve then what else could it be then the mixing valve. It doesn't matter that it's brand new. If you don't have 150 up to the valve then you have to trace it back.
Right. But it’s the second mixing valve to produce the same results. It makes me think that there’s something wrong with the pressure on one side of the valve, but that’s a complete shot in the dark.
 

Jeff H Young

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View attachment 91051
I don't understand the point of anything other than what I have drawn.
You eliminate 2 check valves and extra piping thats a good thing ! but he had a working system I dont see how that caused water to be at a 99 degree max . 150 degree water at the valve and 99 coming out makes me wonder if there is almost no flow at the valve . Assuming a good valve and equall pressure the water has to mix but if the hot line is plugged near the mixing valve maybe it would not reach the 120 setting or what ever you set it at also asuming its cranked all the way up
 

Chesterton

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I don't understand the point of anything other than what I have drawn.
OK. The hot Webstone EXP E2 valve has a very slow drip at the main (yellow) shutoff. I was thinking about replacing that (although it appears that I have to buy the whole kit). In the absence of other ideas should I simplify the plumbing to this (see image)?

Another thought: Could there be air in the system somewhere causing trouble? I drained everything to solder the fittings for the new mixing valve (the old one was solder rather than union) and refilled with hot faucets open. At this point we've used hot water everywhere in the house...
plumbingDiagram2.jpg
 
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