Boiler Blues :(

smithfan

Specs:
Triangletube Solo 110
Primary/Secondary
4 circulator pumps. 1 inside boiler, 3 managing zones.
2 baseboard zones, 1 in-floor slab zone, preceded by mixing valve.

I'm at the end of my rope trying to figure out this boiler problem. I've attached pictures. Basically once or twice a year the Baseboard(zone2) circulator will stop pulling/pumping water into the zone. It's a grunfos 3 speed and is still running when this happens. This winter it's already happened 3 times, so the problem seems to be getting worse. I've fixed it 2 different ways. One way has only worked once, the other way has worked every time.
Yesterday with both baseboard zones calling, I turned the pump speed of the problem zone from low to medium and then it did pull the water through and heated the zone. Almost like a magnet was holding it back!
Unfortunately, today this didn't work. I came home and no heat again in that zone. I turned off all other zones so it was the only one calling for heat, and it still wouldn't pull through, instead my boiler overshoots it's setpoint believing there is flow through zone 2 ramps up past 200 degrees because of the super hot primary return water.
This can't be good! The only full proof method I've done to fix this the problem is isolate zone 2, turn on the fast fill and purge the thing..Then it works fine again, almost like it was air bound or something.
The only thing I can think is my piping arrangement in my secondary loops have too many 90 degree bends, or there is some flow issue. I'm open to any ideas. I ramped up the boiler pressure to 20 psi from 15psi to possibly try and help move any air out of the system. I just don't know where to go from here. I am an 1st year HVAC student, unfortunately Hydronic Heat isn't until year two!

Jamie Hall

You are asking a lot of those pumps. I would be very suspicious that your are very near, or below, the required net positive suction head on the offending pump, which can easily cause the pump to become vapour bound, if not air bound.

It would be much better if the piping from the pressure tank which I see off to the left there to the pump suctions was much more direct. Might not solve the problem, but surely wouldn't hurt.

Danny Scully

Well one thing I’m noticing is that you’re closely spaced tees are reversed on that zone. I’m seeing zone 1 as supply return, then zone 2 is return supply, then zone 3 is supply return again...

smithfan

I noticed that too! Didn't know if it was an issue or not?

Zman

That is one of the wackier piping arrangements I have seen. Aside from the primary/secondary gone bad with diminishing temps to each zone, your zone 2 is piped backwards. It is pulling in it's own return mixed with whatever water is passing by in the main loop. Someone get the sawzall!
As far as your air lock issue, it is hard to say what is causing it. Proper piping would likely fix the problem.

Paul48

Does that thermostatic mixing valve over-shoot it's setting?

Ironman

The secondary circ (zone 2) is fighting the boiler circ. Get you Tees right and it should work.

Didn't we see this, or one very similar, a year or two ago? I remember commenting about the backwards connection then.

Your spacing between the Tees and the near Ells is too close, also.



In your scenario, the boiler is pumping straight through the Tees and the zones are coming off of the bull of the Tees, but the fluids don't know any different.

Also note: the arrow going to the Tee that says "boiler hot supply" is pointing the wrong way in the diagram.

I'd highly encourage you to get Dan's book on "Pumping Away" from the site's bookstore. Once you digest it, you'll be leaps and bounds ahead of your hydronic classmates.

smithfan

I had an "hvac" company re-do the piping a few years ago because it was worse when I bought my house. The wacky arrangement is mainly so they could get everything to reach the existing pex/copper in the ceiling. That's why you see all the weird bends and such. So what I'm gather is it should be piped of the primary: supply/return, supply/return etc...Also, maybe the pumps should be closer as well.

Zman

Yes, the supply/return, return/supply was the problem I was referring to. That is a major issue.
Honestly the arrangement is just a bad way to do it.Unless there is some reason you want colder water going to zone 2, I would just repipe the whole thing.

Ironman

Yeah, we saw it last year and pointed out the problem then:

https://forum.heatinghelp.com/discussion/159176/no-heat-in-1-of-3-zones-air-locked#latest

hot_rod

How many feet of baseboard and pipe on the zones. need to add up all the pipe, ells and fin tube to get a developed length. Either you don't have enough circulator, or air locks that have not purged out.

Also the 3 way thermostatic appears to be mis-piped. The return goes both to the valve C and back into the primary.

Some of the return flow mixes in the valve, some returnstbs

hydro_newbie

Would it make sense to try reversing the direction of the zone 2 circ to see if that makes things better? That doesn't address some of the other issues that were raised.

hot_rod

Best fix would be to correct all the mis piping. The pumps should all "pump away" from the primary loop as mentioned. The 3 way piping needs to be corrected.

HVACNUT

It also looks like they piped both the hot and cold for the radiant mixing valve off the main return. Why?

smithfan

Jamie Hall said:

You are asking a lot of those pumps. I would be very suspicious that your are very near, or below, the required net positive suction head on the offending pump, which can easily cause the pump to become vapour bound, if not air bound.

It would be much better if the piping from the pressure tank which I see off to the left there to the pump suctions was much more direct. Might not solve the problem, but surely wouldn't hurt.

Basically your saying the pumps are too far away from that primary loop?

Jamie Hall

smithfan said:

Jamie Hall said:

You are asking a lot of those pumps. I would be very suspicious that your are very near, or below, the required net positive suction head on the offending pump, which can easily cause the pump to become vapour bound, if not air bound.

It would be much better if the piping from the pressure tank which I see off to the left there to the pump suctions was much more direct. Might not solve the problem, but surely wouldn't hurt.

Basically your saying the pumps are too far away from that primary loop?

Basically.... just that there may be too much pressure drop between the point of no pressure change (that expansion tank) and the pump inlets. Shorter distance helps. Bigger pipes. Fewer fittings...

Harvey Ramer

If you switch those closely spaced tees to the correct orientation, the system will work.

Lets try to explain.
The point of no pressure change is at the expansion tank connection. From that point the the pressure will begin to drop as you move along the primary loop till you get to the inlet of the primary pump. At this point the pressure will increase on the outlet of the pump and than drop off again on it's way to the point of no pressure change.

If you follow that through, you can see that the first tee in question has a higher pressure than the second tee right beside it. Water always flows from high pressure to low pressure.

Now lets look at what you are trying to do with the current arrangement. You are trying to take water out of the lower pressure tee and force it into the higher pressure tee. In order for that to happen, the secondary pump has to generate enough of a pressure difference to not only overcome the pressure drop in all it's piping, but also overcome the pressure drop between those 2 tees.

At first glance, that may not appear like a big deal. But let's examine it a little bit closer. The pressure drop of water coming out of the side branch of a tee is somewhere in the neighborhood of 5' equivalent pipe length. Putting water into the the side branch of the tee requires substantially higher available pressure. The available pressure to do this in properly oriented closely spaced tees comes from both the secondary pump and the naturally decreasing pressure in the primary loop. In your case, the secondary pump has to overcome all the pressure loss on it's own.
Not only that, but let's say for example, the primary loop is moving 10 gpm and the secondary loop is moving 3 gpm. When you come to the first tee, you have 10 gpm entering the run. The secondary pump is then trying to cram another 3 gpm into the branch of the tee. This equals 13 gpm coming out of the run of the tee and entering the second tee. The velocity increases from 3.91 ftps to 5.08 ftps between the tees. Not only does the increase in velocity create more friction loss, but increasing velocity itself in a turbulent arena requires a good bit of energy/pressure.

Your secondary pump has to do all of this work.

Not to mention, any air coming out of the secondary into the first tee, can recirculate right back into the secondary on the second tee.

HVACNUT

Are the connections to the radiant mixing valve correct? Both cold and hot coming from the return?

smithfan

Very insightful info guys. This is exactly why I'm going to school for HVAC. 2 different companies worked on this boiler and neither of them got it right. The way the mixing valve is set up has always bugged me too. Yes, I did post this question last year, but it had only airlocked that one time and the problem didn't return until this winter. At this point there isn't anyone in my area I'd trust to do the re-piping, so I'll just wait until I get through my hydronic heating class next year and do it myself.

Ironman

Why wait? You can do it. Pipe it like this and it will work fine:

The only difference is you have 2 high temp zones and one low temp.