Air keeps getting in hot water fin tube

[BronYrAur]

I have a situation where air keeps getting in a piece of hot water fin tube. This is a piece of perimeter radiation. Every once in a while it sounds like a large slug of air is getting trapped in the tube. It knocks and gurgles.

I managed to catch it on video and will try to attach a clip. The thing that completely puzzles me is that the fin tube is approximately 30' BELOW the mains. It has been vented numerous times, but the air keeps coming back.

I don't know much about the overall hot water system. This piece of fin tube was just added to an existing system. I would suspect that they have a problem with the air separator.

If you are able to view the video, please let me know what you think.

 

[kbs]

There appears to be a non-electric zone valve at the end of the line. It sounds more like a valve installed backwards in a system with a high velocity. Non-electric valves will hammer closed repeatedly if backwards. Turn the t'stat on the valve all the way up when it is banging. If the banging stops, this is probably your problem.

 

[ChasBean1]

Every high point (even in a rise/drop lower in the system) should have a vent and every low point should have a drain. Tough to tell exactly what's happening here.

 

[DrRTU]

I could not see the air on the video (just kidding). Entrained air will take the path of least resistance and will end up stuck in the strangest places. You are correct in your assessment, if the eliminator is working perfectly, the system will flush it’s self. Judging by the picture, the system is old and modified. Hopefully you have not inherited a poor performing system. I bet the owner is stating “ we never had the problem before you added the BB”. If the system is pumping into the return and or the pump is at a higher elevation that could be the source of air.
1. Check the zv for correct install direction.
2. Vent the system again – air may have been admitted during BB install.
3. Check main vents, near boiler vents and air eliminator performance.
4. Install a new vent at the new BB.

 

[TBP]

When the system is bled, do they in fact, get air? I've seen guys continually go back and "bleed air" out of baseboards or rads that never actually vented any air - they just drained enough water to create a flow, and got heat for a short period of time.

 

[RossABQ]

Is the actual BB coil installed level, or sloped the wrong way?

 

[willard3]

You have water hammer, not entrained air. The water in the radiation must be running at very high nelocity to hammer like this.

I'll guess the control valve is faulty.