Dual setup AO Smith Hybrid water heaters

[Rainer]

Good evening Team- I had another post I believe i've corrected it- Now i'm into the heart of the problem- I have two AO smith hybrid water heaters ran in parallel- Lets call Heater left A and heater right B- A was brand new and installed in my other house and ran for 4 years no issues- B I bought scratch and dent and needed a few parts to get working-

Fast fwd new house install both and only A is running and running non stop- I find out that it's at 136F for temp- B water heater has hot water going to the cold pex- This evening I turn A off and test B running and after running most water out B comes on like it should- what's the problem was temp to high- do I need to install check valves.. Help!!!

 

[Reach4]

Are you saying that the hot of B goes to the cold of B, or are you saying that the hot of B goes to the cold of A?

Maybe make a diagram/sketch.

If you are doing passive recirc, you would need an easy-open check valve. If doing pump-driven recirc, I think you need a check valve, which could be part of a component of the recirc system.

 

[Sponsor]

 

[Rainer]

https://photos.fife.usercontent.goo...VcE_9X_bI6GOJ6xA=w710-h947-s-no-gm?authuser=0

 

[Rainer]

https://photos.fife.usercontent.goo...VcE_9X_bI6GOJ6xA=w710-h947-s-no-gm?authuser=0

 

[Reach4]

So parallel, as you said. If you stay parallel, you will need to add a valve, probably a ball valve, in the cold line of the one that is doing all of the work. Partially close that valve. Tuning the amount of closing will take a lot of trials. However both should have ball valves anyway. In fact maybe add 4 ball valves (inputs and outputs) to let you take one out of service.

More usual would be to put these WHs in series. That takes care of balancing.

PEX needs supporting every 32 horizontal inches. If you have city water, you need a thermal expansion tank (not the smallest either). So add some support (wood or Unistrut or generic strut) to attach the pipe hangers, and to carry the weight of the the thermal expansion tank. You should probably also have a mixing valve to keep water hotter than 120 from being sent to tubs, showers, and faucets.

https://www.supplyhouse.com/sh/control/search/~SEARCH_STRING=sharkbite valve

https://www.menards.com/main/search.html?search=strut
https://www.menards.com/main/search.html?search=push+valve

 

[Fitter30]

To make them parallel the take offs have to be the same lenght. The correct way is to pipe them first in last out reverse return. Different size heaters doesn't matter or age difference this keeps the pressure drops out of the picture. In the diagram need valves on both ins and outs incase one heat has a problem or leaks.
kcwaterheater.com/water-heater-piping/

 

[Master Plumber Mark]

Parallel will not work properly with all those bends ....... it never will pull evenly and correctly....

I would suggest you run them in series into one and out through the other one and then
both will have to heat the water that passes through them


also on another note that blue Rhino carbon filter or whatever it is is a peice of junk
and is not helping the situation