Can a Plumber tell me what this is?

aigomorla

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We got a tankless water heater installed, and the plumber installed this device saying it would make our hot water come out faster.
It does not look like a recirculator that we had when we had a tank system.

Instead what it seems to do is make my cold water upstairs extremely hot.
I am unable to mix cold and hot water upstairs sometimes, as i think this unit is feeding the cold waterline hot water.

Can someone tell me what this thing exactly is? And if its the root of my problems of not being able to control the hot water / cold water ratio upstairs.

20220919_233800.jpg
 

NutBucket

Lifer
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Looks like it is thermostatic bypass valve. I would guess there is a pump built in to your new tankless. I wouldn't remove it unless you can disable that pump.
 

aigomorla

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Thank you.
Reading the tech sheet it says it should be installed at the furthest plumbed unit, which is definitely upstairs and not the starting unit, which was the downstairs bathroom.

I am going to reinstall it upstairs and see if this will fix the hot / cold water mixture.

BTW, tankless water heaters are absolutely horrible. I regret every moment of having it installed. I would probably have it pulled and replaced to a tank heater if not for the new permits required to do so.
But i miss my old 70Gal tank water heater.
 

waffleironhead

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Aug 10, 2005
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That unit looks like more hassle than anything. I'd just ditch that thing. It definitely is dumping hot water back to your cold lines. Unless, you absolutely require having hot water instantly at the tap(IE would rather waste elec/gas over wasting water).
 

Motostu

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Oct 5, 2020
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We love our tankless (16+ years now). Don't have a return line or a valve like that, though. Just have to wait for hot water at the furthest taps.
 
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aigomorla

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That unit looks like more hassle than anything. I'd just ditch that thing. It definitely is dumping hot water back to your cold lines. Unless, you absolutely require having hot water instantly at the tap(IE would rather waste elec/gas over wasting water).
That was the issue i was having.
It was dumping hot water in the cold water line, so i couldn't mix the hot water with cold water properly, and the showers would get scolding hot.

I moved it over to the furthest tap, and so far i think its working ok.
But if i still have issues with hot water and cold water mixing, i may just get rid of it, and use the heaters internal tank instead, althouigh its only 1 gallon.

We love our tankless (16+ years now). Don't have a return line or a valve like that, though. Just have to wait for hot water at the furthest taps.
Supposedly the unit i have has 2 different types of reciculation.
One is with that tool i listed up top for large houses.
The other is a internal 1 gallon.

I honestly think the house is too large for a tankless.
The 70 gallon tank we had was so much more reliable and the recirculation pump on it, worked flawless at the hours it was set.

This tankless is giving me headaches in taking showers.

Definitely will not go this route anymore, unless possibly its a small house.
 

sdifox

No Lifer
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Those things are usually installed for tank system, not tankless. I doubt it makes any sense in a tankless system.
 

Greenman

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That was the issue i was having.
It was dumping hot water in the cold water line, so i couldn't mix the hot water with cold water properly, and the showers would get scolding hot.

I moved it over to the furthest tap, and so far i think its working ok.
But if i still have issues with hot water and cold water mixing, i may just get rid of it, and use the heaters internal tank instead, althouigh its only 1 gallon.



Supposedly the unit i have has 2 different types of reciculation.
One is with that tool i listed up top for large houses.
The other is a internal 1 gallon.

I honestly think the house is too large for a tankless.
The 70 gallon tank we had was so much more reliable and the recirculation pump on it, worked flawless at the hours it was set.

This tankless is giving me headaches in taking showers.

Definitely will not go this route anymore, unless possibly its a small house.
There isn't any reason your tankless shouldn't work just as well as your prior unit. Though I find the use of a recirculating pump that uses the cold water line to be a questionable practice. The heater is going to be firing several times a day for no reason.
 
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iRONic

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Those things are usually installed for tank system, not tankless. I doubt it makes any sense in a tankless system.
Huh?!?!

I've never seen one installed for a hot water heater system in the US. The tank energy source (gas,electric) fires all day long regardless of your demand because the internal thermostat setting keeps the tank water at a certain temperature.

Since an on demand system does not fire until a faucet is opened the static water in the lines will be cold.
 

sdifox

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Sep 30, 2005
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Huh?!?!

I've never seen one installed for a hot water heater system in the US. The tank energy source (gas,electric) fires all day long regardless of your demand because the internal thermostat setting keeps the tank water at a certain temperature.

Since an on demand system does not fire until a faucet is opened the static water in the lines will be cold.
Same thing happens with a water tank system. the water in the pipes will get cold over time, so the idea is to cycle that water back to the tank. Not a great use of enegy but even more pointless on tankless. Only place it makes sense is multi unit buildings with central boiler.
 
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NutBucket

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Aug 30, 2000
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On a tankless I'd want a system with a button. Want hot water? Push the button and the pump fires to speed hot water delivery. On larger houses I've seen multiple water heaters installed to mitigate the issue.
 

sdifox

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On a tankless I'd want a system with a button. Want hot water? Push the button and the pump fires to speed hot water delivery. On larger houses I've seen multiple water heaters installed to mitigate the issue.
that makes zero sense for tankless, how is there going to be speedy hot water delivery unless you clean out the water that is already in the pipes?
 

iRONic

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Same thing happens with a water tank system. the water in the pipes will get cold over time, so the idea is to cycle that water back to the tank. Not a great use of enegy but even more pointless on tankless. Only place it makes sense is multi unit buildings with central boiler.
OK, I was only referencing a residential house.
 

NutBucket

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that makes zero sense for tankless, how is there going to be speedy hot water delivery unless you clean out the water that is already in the pipes?
Why? Push water through the hot side back into the cold but only on demand. It would work just fine.
 

sdifox

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Why? Push water through the hot side back into the cold but only on demand. It would work just fine.
You don't have hot water ready to go on tankless. For tanked system you are going to increase water tank fire rate slightly plus pump energy use. In a home setting it's not very useful.
 

NutBucket

Lifer
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To have it be a button you push when you want hot water? It would basically be zero waste. Am I missing something?
 

sdifox

No Lifer
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To have it be a button you push when you want hot water? It would basically be zero waste. Am I missing something?

Are you talking about tankless or tank system?

There are under counter instant hot water systems but they are not high volume.
 
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NutBucket

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Doesn't matter. My friend had/has a system like that at his place. There's a button mounted on the vanity that kicks on the recirc pump to get hot water moving.
 

sdifox

No Lifer
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Doesn't matter. My friend had/has a system like that at his place. There's a button mounted on the vanity that kicks on the recirc pump to get hot water moving.
The ones on vanity is the under-counter mounted hot water system I was talking about.

Example not recommendation
 

aigomorla

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No we have a whole house NAVIEN system.

Video on what that thing exactly does.... but im wondering at what extra cost....
And ur right about it dumping warm water down the cold lane.
I think i am gonna just pull it off.

Doesn't matter. My friend had/has a system like that at his place. There's a button mounted on the vanity that kicks on the recirc pump to get hot water moving.
upon googling... its a dip switch i need to turn off and on, and a bypass valve if i want to ditch that reciculating pump.
But it does give extremely fast hot water.... but it makes my cold line warm.
 

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