Circulation issue- lp boiler
hi folks- I had a brand new LP system installed (Viessmann 120). Upon commissioning the unit, tech discovered we had no circulation to either of the 2 zones. DHW works great and the boiler fires right upon command- just can’t get water past the Grundfos pumps. They are powered and sound like they are turning, but no hot water getting past either. He purged the system and found great water flow through it. Presumably no blockages. We’ve decided that we just had bad luck with two defective pumps out of the box and will be replacing them Monday am. Any other creative ideas out there as to what it could be other than the pumps? He seems to have pinpointed those and found no other problems. Ignore the dhw tank, it’s shut off
Comments
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It needs purge valves on the returns above the ball valves on the system side of the separator. With the purge station on the boiler side, it's just purging through the boiler.
2 -
Is enough air out of the loop for it to circulate? the circulator can't push the water through an air pocket. The pressure difference from the water supply to the open drain can push through it so purging could still leave a pocket of air somewhere that the circulator can't move water through.
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we assumed so, ran probably ten gallons through it until it was coming out with no air bubbles. I could see maybe one zone having an air pocket, but both seemed improbable. The hi-vent on the separator was letting off some air afterward. I guess it’s possible there’s still an air pocket in both zones somewhere. Not one radiator heated up though.
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Maybe I'm ,missing something, but I don't see any way to purge the zones individually without running water through the separator — and the boiler. Which won't help at all.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England2 -
A fairly easy update would be two Webstone purge ball valves installed where the white handle valves are.
I'm not sure there is any air removal function inside the LLH? Many Viessmann installers prefer a 4 in 1 separator for dirt, air, magnetic and hydraulic separation.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Sometimes the IFCs can be installed backwards into the pumps. It would cause no flow situation like you see.
2 -
The boiler is plumbed on the primary and can be isolated before purging.
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Make sure the circs are not installed backwards. I would think you could isolate the boiler and add a purge valve on to the spare return manifold connection.
The air vent on the LLH should take care of the rest.
I doubt the circs are bad.
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"Occams Razor" says that it its very unlikely that you have TWO bad Grundfos circulators right out of the box. Like others have mentioned: put some purge valves on the return manifold of the system side of your LLH. The boiler side of the installation has ALL KINDS OF purge points. The system side is hydraulically separated from the boiler side. It TOO needs to have purge points. Put them in. And then purge. Voila!
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How? The only purge station I see is on the primary return. The make-up water goes into the separator. If you isolate the supply and return on the primary loop, how are you forcing water through the secondary loops?
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that’s sound logic. I did some light vibrating on various spots of the first floor run of pipes. Actually heard a bunch of gurgling and went down to the unit and the hi-vent on the separator was spewing air. The zone started flowing nicely! I have this theory about my fill water: I have a whole house filter before the system, the water that comes out (in sinks, and anywhere else) is ‘milky’ with microscopic air bubbles. This is a side effect of the filter in place. If you were to fill up a glass, you’ll see all of the microscopic bubbles eventually go away. My theory is that when I fill the boiler, these air bubbles turn into large ones and make it a pain to purge from the system.
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I think I misunderstood what I have. Thanks is for the clarification. I assumed since we could isolate the boiler from the heating loop, that this is what you were referring to.
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Tech came here this morning and added purge valves…worked like a charm. The whole second floor was airbound. Thank you!
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