I have noticed that often when the circulator shuts down a whistling
noise is heard for a moment. Can someone comment on what is causing
this to happen?

Recently, a baseboard radiator heater was replaced and I did attempt
to bleed the series loop at the boiler. Could this whistle be an
indication that there are air pockets remaining in the closed loop?
Prior to the radiator replacement I do not recall ever hearing the
whistling sound.

Thanks

de ~ Vince ~
Long Island in New York

Vince wrote:
I have noticed that often when the circulator shuts down a whistling
noise is heard for a moment. Can someone comment on what is causing
this to happen?

Recently, a baseboard radiator heater was replaced and I did attempt
to bleed the series loop at the boiler. Could this whistle be an
indication that there are air pockets remaining in the closed loop?
Prior to the radiator replacement I do not recall ever hearing the
whistling sound.

Thanks

de ~ Vince ~
Long Island in New York

Likely a bearing failed on circulator and/or the motor. Fill the
filler spouts with oil several times during the season. Maybe you can
nurse it along 'til summer.

Do you have a water auto feed valve, if so turn it off see if still
occurs. May be a leak at the relplaced radiator.