Persistent Air Problem Indirect DHW-

ced48

I have an ongoing issue with air in the indirect loop of a Lochinvar WH55. It is a simple loop with a circulator. Static pressure is set on the high side, maybe 16 pounds. When finished with the cycle, the pressure builds to about 20 pounds, with water temperature in the boiler, 160 degrees or less. The tank is a HTP 20 gallon. After raising the pressure to where it is now, I went a month or more without any noise, now, I get a little air noise towards the end of the cycle every so often. The boiler is in my den, so I can hear every peep it makes, so I'm sure it only has the problem sometimes. My question is how in the world can I go weeks with no noise, and then get the noise back. This is driving me crazy. What am I missing? Why do indirect loops not need an air separator like the heating loop requires? Do i raise the pressure even higher?

icesailor

Large Stationary diesels run with "B & A"
Pumps. Before and After pumps. With a "Normal" start, the "Before" pump comes on and circulates fluid before the engine starts and circulates water throughout the engine. When the engine stops, the pump continues to run "After" shutdown to remove any hot spots in the engine.

Your boiler might be overheating after shut down. Maybe your boiler pump needs to run for some time after the burner and call end to scavenge extra heat from the boiler. If it is just for domestic hot water heating, the boiler should be running on "High Limit" and thermal lag is causing hot spots that don't get removed after the pumps shut off. Try turning the boiler high limit down to 170 or 160 degrees and see if the problem gets better. If it does, see if there is a way to make the boiler pump stay running. Are there positive shutoff zone valves and they can isolate the expansion equipment from the boiler when closed?

Something to consider.

ced48

Yes, I can isolate the indirect loop from the heating loop. The boiler never heats to more than 160 degrees. The problem starts to develop at 140 degrees, with very brief and tiny burst of sound. Then, with temperature above 150, a louder bust of gurgles and swishes, maybe happening once or twice, till shutdown at 158 degrees, or so.

remodel

ced48, do yo have any high points in the DHW loop? does your DHW loop go through an air-removal device? if so it might not hurt to put an auto-air vent in.

ced48

The piping comes out the top of the heat exchanger, out the bottom of the boiler, down to a circulator, and down to the tank, then back up. Space is really tight, but I think I could fit one under the boiler, before the circulator. I have not done this because all the piping diagrams I have seen have no air separators shown, and I hate to add one and then find out it was something else-but it might be the answer, thank you-Lets see if any one else has any ideas-

Don_197

Is the bursting noise you are hearing coming from within the boiler jacket or the HTP Indirect tank? If it is within the boiler jacket, I am betting you have a boiler with a Gionanni heat exchanger (HTP ModCon, Munchkin, or Lochinvar Knight.....there are a few others with it too) and this is the sound of STEAM FLASHING. That would mean you have a restriction in the heat exchanger, which may or may not be cleared by a chemical forced pressure flush. Can you tell us more about your system? What kind of boiler?

Jean-David Beyer

I have a W-M Ultra 3 and one of their tank within a tank indirects. The Indirect has a little automatic air vent valve at the very top. The loop to the boiler comes out the top of the boiler over to the bottom of the indirect. It comes out near the top of the indirect through a circulator back to the boiler. There is no air scoop or microbubble eliminator in that circuit. There is a microbubble eliminator in the P/S loop that heats the house.

Now in theory, any air that has not been eliminated from the system by the microbubble eliminator should collect in the top of the indirect until it gets enough to open the automatic air vent. But once in a while, I hear air noise when the indirect is calling for heat. That air vent works if I open it by pushing done on the relief. The cap I leave open 1 1/2 turn. When I open the vent, I usually get water immediately, but once in a while I get a little air.

I run the indirect at 170F in, and the pressure at the top of the boiler is between 13 and 15 psi, so I doubt any vacuum is developed to suck in air from the vent valve.

Since, for me, this is not a problem, I do not propose to do anything about it. I think it would make more sense to have the microbubble eliminator in the indirect loop instead of the home heating loop because the indirect loop runs at 170F, where the home heating loop never exceeds 148F (max set at 140F but with +8|-7 range). I have never seen it go that hot. But there is no room for one.

ced48

I'm not really sure where the noise is coming from, but I have heard a Loch flash, and this is not flashing. It is air-

Don_197

On every indirect we install that was not a Triangle Tube Smart Tank (which has a built in air vent at top of HX) we installed air vents at the outlet piping to the boiler. We have spent a LOT of time on startup trying to un-airlock the indirects........to the point where any time we had a choice, we used the TT tank in a tank indirects........almost exclusively for that reason (although the recovery rate is pretty impressive as well.)

ced48

Okay, so I'm not the only guy who has had this problem, fewwww-I was beginning to think I was loosing it-

ced48

I think I'll try putting a Taco 4900 in the short horizontal run that comes just before the pipping drops down to the circulator. I just have to check and be sure I have room. I hope this takes care of this problem once and for all-