Primary loop no flow

CRhoads

I have outstanding flow, in the floor loop of my system, but I cannot seem to get any flow to the primary heating loop when the purge t is in operating position. I believe there is a design flaw in my system that is causing a block, either a check valve in the pump due to pressure not being greater on side then the other. I have about 40 hours of troubleshooting and bleeding the system over the last three weeks. I am not sure what step to take next. Any advice that you are able to offer would be an immense help. The floor loops are all within about 20 feet of 1 another and range from 240 - 260 foot of Pex Al Pex. There are a total of six loops. Willing to answer any questions you have. Thank you.

My current thought is that the UPS 15 pump needs to be on the other side of the pressure tank.

Ironman

The problem is that you’re trying to use a tankless water heater instead of a boiler. The pressure drop is way too high because it’s designed to have 60 psi incoming and an open faucet on the other end.

You need to get the right tool for the job: a boiler.

GGross

Lets start with the most important thing. Is that a takagi tankless water heater? If so you most likely need a larger pump to overcome the pressure drop of the heat exchanger, off hand I have usually seen a 26-99 done for those, but you would need to check with the manufacturers charts. I would also change the primary loop around, you should not put the expansion tank on the discharge side of a pump, and while it never has come up for me before, I would never locate a relief valve directly on the discharge side of a pump like that, not sure if thats a rule, but I would never do that. Either way a pump should be on the return side of that loop, so the discharge side of the pump is flowing into the heater, and the expansion tank on the suction side. I still think the first problem is that you don't have enough pump, perhaps you have some spec on that unit that could shed some light on the matter. Takagi has also generally only allowed their tankless units to be installed in either a DHW only application, or a mixed use application, so hopefully you have gone over that prior to install to confirm the manufacturer allows this to be a closed loop only system .

CRhoads

Thank you @GGross and @Ironman

It is in fact a Takagi 140H - I definitely missed the part where it was not acceptable for Closed loop operation,

Is there a recommended boiler?

I can easily change the loop around I do not think that would be an issue, I will also move the pump larger pump from the floor loop to the primary loop. Maybe that will overcome the water Takagi pressure loss.

Thank you once again.

GroundUp

As the others have said, the 1558 is too small to overcome the head loss in that tankless- and the tankless is the wrong appliance for this job. The circ is also on the wrong side of the expansion tank as you have noted. With that said, as wrong as it is, you CAN just run it as-is with the purge tee closed and have both circs in series. Your 6 loops will have enough flow to keep the Takagi satisfied and the system will operate (as you have seen) until the tankless eventually craps out. Again I am not condoning this because it really should be a boiler, but I am also not a fan of throwing away an appliance that will in fact work for this application until it doesn't. I'm quite partial to the Lochinvar Noble, an 80k unit is more than adequate for your 6 loops and can utilize your existing piping w/ 1558 primary circ, though it does need to be moved to the other side of the expansion tank if you were to change it over.

CRhoads

thank you for the recommendations. Might take me a while to save up for the boiler. I really do appreciate all the feedback and advice i am receiving here.

This has been a very humbling experience.

Snowmelt

it looks like you have to do a few things, switch those pumps out. O thing thing you want to do is increase the copper in your primary loop to a minimum of 1 inch, 1-1/4 if you can.

Put the pump going into the Takagi

Pup the expansion tank and air separator before the pump …..

Add an air separator on other side of pipe. (secondary)

I did a Takagi as an experiment for a snow melt system

Worked well for 12 years till we moved

CRhoads

@Snowmelt - thank you, I will try your advice. Hoping to get enough flow for a few seasons. I would really like to see 1 - 2gpm across the water heater. I do see flow just not enough for the water heater to stay activated. Learning a lot and thank you for the recommendations

GroundUp

Just close the purge tee and run both circs in series. Don't waste another penny on this until you can afford to do it properly with a boiler. This may very well run fine for a decade as-is; Menards sold thousands of Takagi systems piped direct with only the 26-99 and I still see them pretty regularly today, almost 15 years later. They're not "right", but they do work.

Dave Carpentier

Does it matter to have opposing flow directions in the P/S section ?

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1809152#Comment_1809152

Not usually — depends on the two flows

hot_rod

https://forum.heatinghelp.com/discussion/comment/1809152#Comment_1809152

unless the primary and secondary flows are and always stay the same, there can be flow reversal between the tees

Dave Carpentier

Thanks, makes sense now that I think more (lol, I have buffer tank brain and not p/s). So no matter what flow rate is in a secondary loop, you're always going to transfer the primary's flow rate worth of heat into it.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1809166#Comment_1809166

The buffer tank, piped like this, establishes a P/S and offers the buffer capacity of the tank.

The large piping size at the tank is where the low loss header aka P/S is happening.

The flow rate any circulator is moving at any given time determines what is flowing through the tank, or close spaced tees in P/S.

So multiple benefits from a buffer besides a "thermal battery"

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