metallic noise from circ area and from baseboard

Nom_Deplume

Hello...our hot water heating system has developed a faint but increasing "tinkling" metallic noise from some of the baseboards. The same noise can be heard at the circulator that drives these baseboards. In a stupid homeowner move, I replaced the circ (I had an extra one). It made no difference.

However if I turn the circ off while leaving the other circs on, the noise stops.

(a) Is the next possible culprit the check valve that I know is built into one of the isolation valves?

(b) How does one tell which valve has the built-in check valve?

(c) Why do I need a check valve at all? Our primary/secondary system has three circulators, i.e. two zones. The zones are so well-matched that I use one stat for both zones, with no over/under-heating. In other words the primary circ and two secondary circs all run at the same time. They run 12 or more hours a day (outdoor reset) for most of the season. No DHW. So why do I care about ghost flow?

Thank you!

Jamie Hall

Possibly a small amount of air in the system. Check the pressure and the expansion tank and any air removal device.

Nom_Deplume

Thanks for the suggestion!

There is a Honeywell Supervent, but it is on the primary, and the noise is in a secondary (no noise if I run everything except this one secondary circ).

I have drained lots of water from the baseboards and do not know what else could be done to remove air.

Jamie Hall

If you drained water from the baseboards and didn't keep the pressure up while you were doing it, you may have introduced air. It's possible that -- eventually -- the Supervent will do the job, but you may have to actually purge the loop.

Nom_Deplume

Homeowner, but not so ignorant as to drain without leaving the fill valve open.

PS I figured out the answer to my question (b)---one valve has a longer body than the other, and it must be the one with the built-in check valve.

mattmia2

introducing fresh water in to the system will introduce the air dissolved in that water so the air elimination will need to remove that air.

EBEBRATT-Ed

If you have a flow check valve they usually have a lever or screw co you can open it and see if the noise goes away

Nom_Deplume

Just an update. Of course it was not air making the metallic noise. The check valves built into pump isolation valves do not have any built-in way to lock them open. I jammed the check valve open with a small pellet made of aluminum foil. Noise is gone. I realize the foil pellet is slightly blocking the flow. I will change the entire shutoff/check valve during the summer.