Recirc Pump on Multi unit Tankless system

[David]

Howdy --- Hoping to get some insight guidance. I'm a DIY'er. I have installed a Rheem tankless system; dual unit, using their EZ-Link cable. I may get this wrong, but basically, once one unit hits 80%, it kicks on the second. The EZ-link basically controls this. Everything working great... except recirc. These units have a built in recirc controller, however it does not work in a multi-unit set up. So I hooked up my recirc pump like I would on a tank system; on the recirc line, and on a timer to kick it on for just peak hours. The problem I'm having is that when this pump kicks on, it creates just enough pull in the lines that the tankless unit wants to kick on. However the water flow isn't strong enough, and the unit error codes and sometimes needs to be reset. The error code is P1.
Thoughts? input? How can I get this to recirc? Would rigging up an aquastat help in anyway? I

see attached pic... my late night, couple cold ones, work.

 

[Jadnashua]

Some of the tankless systems that support recirculation have a small tank. That gives the ability to draw from it, and potentially keep the lines to the point(s) of use warm, depending on how it is setup, without having to turn the burner on when the pump runs.

Have you called the manufacturer to see if they even support recirculation with your setup? Some will void your warranty with one, or, it's not installed properly.

 

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[DustinB]

P1 is actually not an error code it means there is a low flow rate. Im not exactly sure which units you have but Rheems I am familiar with require a minimum of .4 gpm in order to fire. With 2 units together that jumps up to .8 gpm unless u have the communication link which you say you have connected. How Rheems alternate with communication link is a bit more complicated than most other heaters. Also, I believe but am not certain that the % of use before one heater will ask the other for help is much lower with the rheems, closer to 30%. Ive been given different answers.

It appears by you pic the cold water comes across and tees for 1st heater, then tee in between heaters for circ line, then continues on to 2nd heater. Hard to tell by pic but if this is how line is run I do not like this set up for a couple of reasons. The direction of flow for cold water is from left to right. So the pump is having to push against the flow direction. I also think the cold line should come up in between the two units for equal distribution. So i would have cold water come up in between units with circ line connect here before split to each unit so flow direction is always towards the units.

Perhaps check the circ pump as well to make sure it can handle the size of your loop and the head pressure or verticle rise of your system. You could try using a smart plug instead of timer and aquastat, but i do not see that an aquastat would help your situation becuz a P1 code simply means there is not enough water passing thru unit for it to fire.

 

[Jadnashua]

In a closed loop, head isn't as much of a problem as in an open one...the water falling back on the return helps to push the water up, so you've only really got friction versus trying to push it uphill and then out. The utility company's pump provides the head to initially fill the pipe, so head is only needed to overcome friction, not gravity.

PUmping water through and thus causing the burner to turn on can make the whole system less efficient. Unless there's a small tank in there somewhere to draw hot water off and limit the cycling of the tankless system, longevity will also be decreased. If the tankless system allows recirculation, it generally will have a specific method that must be followed for efficiency, longevity, and reliability. Failure to follow those guidelines can void your warranty and be detrimental to your wallet!

 

[GregFL2001]

Hey David -

I have almost the exact setup and noted the same issues. We’re you able to get to a resolution here?

Thanks,
Greg