Noise from little air release vent on indirect hot water heater

mrblint

The original system boiler and indirect are about 20 years old, but a year or so ago we needed a new indirect hot water heater, and put the new one beside the boiler and left the original sitting below it. The little air-release vent shown in the picture, installed with the new indirect system, makes a rattling noise whenever the indirect calls for heat and the boiler circulates. It started doing this just a few months ago. The sound is a very rapid percussive metal sound, like a kid who lives down the block and plays in the marching band is out in his back yard doing a drum roll on a metal trash-can lid. When I first heard the sound, I thought a woodpecker was hammering on the metal chimney cap. But it's clearly coming from that little device. The knob on the top is not tightened down. The plumbers who installed the system said to leave it loose. I don't understand how they work, and why the pressurized water doesn't squirt out.

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HVACNUT

That's an air eliminator. You might hear it expell short shots of air now and then, but if it's every time the water heater comes on, then there's probably an issue, or the whole system was never properly purged when the indirect was replaced. What's the pressure on the boiler? Is the valve for the Pressure Reducing Valve open? Any boiler piping going into a slab? Can you check your water meter to see if the dials are spinning even though everything is off?

Larry Weingarten

Hi, A remote possibility is that turbulance in the line is causing the float in the vent to rattle. Adding a nipple under the vent, to put some distance between flowing water and the vent would reduce the turbulance the vent sees. I'd try as long and small a diameter nipple as can be made to fit.
Yours, Larry

hot_rod

that's a high point vent, not really designed to be an air purger. I'm not sure why it would be in a line like that?

Some models have a tab that should stick down into the pipe to help coax the air up. But in a tee like that it would not.

In some cases they can allow air in to the system.

What is the pressure on the boiler? Got a pic of the boiler piping, there should be a central air purger their doing most of the work, and the system should get to a point of being air free.

pedmec

you sure that the rattling is coming from the air vent? i would confirm that is coming from the air vent but my prior experiences are that the flocheck is most likely causing the issue. the tongue of the air vent is not in the stream of flow. If you do confirm that it is the air vent i'd like to know what circulator is in the system.

Intplm.

That high-point air vent probably isn't the source of the noise you are describing. It might be related but not the issue, or at least not the entire issue.

Your system probably needs to be purged of air. An air purger should be installed on your system. Hopefully a micro-bubble air purger. A manual purge also would need to be performed. If air is somehow getting in. That also needs to be corrected.