Boiler puzzle

[lbob]

Hello,

I was hoping someone could help me out with a problem I'm having with my boiler. I just had a Navien tankless combination unit installed, and I'm having trouble getting sufficient heat to all parts of the house. I have three zones in my house, one for the kitchen and four season room (zone 1), one for the main floor (zone 2), and one for the newly added second floor (zone 3). We've just finished renovating a previously unfinished attic and installed baseboard heat up there. Everything was working fine in the other two zones, but as soon as we added zone 3 into the mix the other two zones couldn't hit their target temperatures. I've attached a picture of the plumbing as well as a schematic, as it's a bit hard to see all the piping in the pic. The supply line hits zone 3 first (upstairs), then zone 2 (main floor) and finally zone 1 (kitchen/four season). In terms of performance, the upstairs gets heat fine, the main floor is about 3 degrees below target and finally the kitchen/four season is about 6 degrees below target. There seems to be a relationship between the order of the zones and the heating capability. When I isolate the upstairs (zone 3), everything works fine again in zones 1 and 2. Based on the picture and schematic, is there a problem with how this is plumbed? Would that be the reason I can't make the target temps? Any help/advice would be appreciated.

Thanks.

[Dana]

The returns from radiation need to be plumbed to the return manifold, not just a teed loop on the supply side of the world. As-diagramed whenever zone 3 is running it's lowering the temp of the water fed to the down stream zones on the supply manifold.

[lbob]

Hi Dana,

Thanks for the response. Just conceptually, is the following schematic what would have to happen? Basically all three of the returns should tie together and come in to the return line at a single point?

[jadnashua]

Not certain on the symbology, but unless those valves between supply and return are check valves, zones 1-2 will be pulling partly from the cooled return water from the first zone (#3). Not sure you need those legs. You may also need a check valve to prevent returning the water to a secondary loop. It looks like you're trying to produce a primary/secondary loop system. To do this, the takeoff and returns need some very specific locations, separations from each other to work properly.

[lbob]

Thanks jadnashua,

I'm talking this through with the plumber, so I'm just trying to get some second opinions. None of the valves are check, just isolating. Would the best/easiest thing to do be to break the connection between the supply and return loops like the following? Would it be even better if those isolating valves on the return loop were check valves to prevent returning water flowing into the other loops? Thanks for all the responses.

[Dana]

Thanks jadnashua,

I'm talking this through with the plumber, so I'm just trying to get some second opinions. None of the valves are check, just isolating. Would the best/easiest thing to do be to break the connection between the supply and return loops like the following? Would it be even better if those isolating valves on the return loop were check valves to prevent returning water flowing into the other loops? Thanks for all the responses.

If the boiler didn't have it's own internal pump driving the primary loop the above schematic would work fine (with the addition of check valves), but there may be problems with this approach (which WAS where I was going before consulting the manual.)

Backing up a bit to your first schematic...

The manual seems to insist on primary/secondary plumbing using closely spaced Tees for the zones, which appears to be how you've done it. See p. 24 of the manual- that's pretty much it, right?

Almost: Schematically yes, but looking at your photo (rather than the schematic) it appears you're secondary loops are returning water from radiation to the supply manifold side of the web/branch and pumping from the return manifold side. In this configuration it's guaranteed to be mixing cooler returning water into the supply for next zone. The branch connection to the zone pump needs to be closer to the supply than the return loop Fix that and I think yer done. You can try just backing off the flow on zone 3 with the 3-speed pump (or even some ball-valve tweaking so that the primary flow is much higher than that for zone 3, but I doubt that's going to cut it.

[lbob]

Hi Dana,

Thanks for the thorough response, and for taking the time to actually find and consult the manual. Looking at their schematic, the way he's set it up does seem to be consistent with the drawing. I'll make a note of your suggestion and discuss it with him when we're speaking next. Thanks again.

[BadgerBoilerMN]

The piping does not follow any manual. You have what amounts to 3 by-passes and will have a time trying to figure out where the water is going.

You will have to balance flow with the return ball-valves. If all zones are same design temp you may do this with all calling and by feel.

If not, follow installation P/S piping schematic.