Knocking In Pipes / Hearing Flow - Time To Purge?

JustinS

Not sure exactly when it started but I think it's within the last couple of months - don't recall hearing it last winter when the house was new... whenever the heat comes on in one of my zones, there is a loud rapid knocking noise from one corner of the room... it sounds like it's coming from within the floor... this quiets somewhat over time but doesn't really ever go away completely...

Also, I can hear when the heat is on in this particular zone - a soft hum of sorts... often, I can also hear when it first comes on, not sure if it's the circulator coming on but it's a one time event that's followed by the constant soft hum...

I've read around that these could be two signs that I have air in that zone somewhere - I do know that there is some air near the boiler because I can hear some gurgling (not constant but often enough)...

I'd like to try purging the problematic zone - it's the far right zone (closest to the drain)... I think that I should close off all of the other piping? Should the zone circulator be running but the boiler turned off when purging just a zone?

unclejohn

Is the zone heating? If it is it may just be the pipe expanding. If you do need to purge shut off all the pumps and the other zones.

hot_rod

You have a very good air separator, if all the zones flow, that device will grab all the bubbles over time.

Occasionally the little vent hole on that brand plugs up and they don't vent properly. Look for a small hole at the top on that protrusion. Take a paperclip and be sure the opening is not plugged.

The float mechanism inside can hang up on debris also, gently tap the outside of the brass body.

The noise you describe sounds like expansion noise as the pipes warm, rubbing on framing or if the holes thru the floor were drilled to tight.

You have good isolation valves, close all but the zone with the noise and purge that loop.
Be sure the fill valve works properly or you will drain down the system. AND if it sticks on, the fill valve can over-pressurize the system after you purge, keep an eye on the pressure gauge.

Nice that it was insulated, all systems should be.

JustinS

Yes, the zone is heating... I did think that it could be pipe expansion but wondered why it would seem to be a relatively recent development...

So when purging, the water will work its way past the circulators so they don't need to be running? So if I want to purge just one zone, have valves to boiler and other zones closed? If I want to purge boiler, leave it open?

JustinS

hot rod said:

You have a very good air separator, if all the zones flow, that device will grab all the bubbles over time.

Occasionally the little vent hole on that brand plugs up and they don't vent properly. Look for a small hole at the top on that protrusion. Take a paperclip and be sure the opening is not plugged.

The float mechanism inside can hang up on debris also, gently tap the outside of the brass body.

I'll take a look at that soon, thanks for the suggestions...

hot rod said:

The noise you describe sounds like expansion noise as the pipes warm, rubbing on framing or if the holes thru the floor were drilled to tight.

Yeah, I thought about that but as I look back on pictures I took during construction - I see that little plastic "collars" were used extensively as the pipes passed through framing... I don't have any pictures of the problem area but given that those that I do have don't have any piping passing through framing without these...

hot rod said:

You have good isolation valves, close all but the zone with the noise and purge that loop.
Be sure the fill valve works properly or you will drain down the system. AND if it sticks on, the fill valve can over-pressurize the system after you purge, keep an eye on the pressure gauge.

Nice that it was insulated, all systems should be.

Yeah, insulating it was one of the first things I did this past spring/summer once it was warm... I wish the builder had insulated inside the walls (particularly, my DHW recirc) but alas...

unclejohn

Things settle over time and that could be your knocking sound. If that zone is heating I would leave it alone.