Circ noisy on startup

Dave M

I have a boiler with 5 circulators, 4 for space heating and one for indirect DHW.

One of the circulators for space heating makes a water cavitating/rushing sound only for 3 or 4 seconds when it first starts to run. It mostly only does this if this circulator has not run for some time. Once it has run for bit and stops you don't notice any unusual sound the next time it starts. It's worse if it were to not run a for a week. The other 4 zones never do this. Just this one zone. It is the shortest zone (about 20 feet of fin tube, servinf one room). I don't hear any air in any of the zones, it's all quiet. Just the startup noise. The pumps are on the return side (I know pumping away is better and why) but the installer did it this way. It seems to me this pump shuld be as quiet as the other 4. It's not mechanical noise, it sounds more like rushing/churning water as it speeds up. But no sound of air going thru the system. It's as if the body of the pump is a low pressure zone and air is parking there. Or is the impeller bad? Sorry to be long winded, just trying to provide as much info as I can think of.

STEVEusaPA

could ya post a pic

I would like to see how this zone is piped in relation to the other zones.  Do you hear the noise when only this circ comes on, and no other circs are on?  Or do you hear it when other circs are on, then this zone comes on?  It could be a bad impeller.  Do you have isolation flanges on these circs?  If so, swap it with another, see if you still hear the noise.

btw, whats the system pressure, and does it change when the pump comes on?

Dave M

circ noisy

The circulators are all in line on a black iron manifold. I hear the noise regardless of whether other circs are running. I do have have isolation flanges on each circulator. It runs quiet after it starts so I haven't pursued it further yet. I was going to wait until after the winter heating is past. (Maine) System pressure is stable around low 20's. The expansion tank is a 60. I leave make-up water off and the system is pretty air free.

billtwocase

sounds like

you have IFC circs, and that one has issues. Do you hear that noise only at the pump, or throughout the zone?

Dave M

Circ noisy only on startup

There are external Taco flo checks and these are regular pumps, no IFC. The brief duration churn sound telegraphs through the zone. It's not hard to hear, it's pretty loud for a few seconds when the pump first starts. Then it stays quite. There's no mechanical noise from the pump. I'd say it's air. But it's different than the sound you get when you just have air in the system and you hear the air moving through the zone. That's not the case.

billtwocase

then, sounds like

the cartridge needs replacing, or flow check sticking? Pics might help