Might you have a defective check valve, air vent or other component such as a differential pressure bypass valve or zone valve control? Is the expansion tank properly pressurized? Do you have just 1-circulator and is it a single speed or multi speed?

Have you tried closing the zone valves for the basement & 1st floor and then bleeding the 2nd floor zone when the system is at operating temperature?

Just wonderingâ¦

SR

Hello SR,
The only check valve is on the make-up water, no differential, expantion tank is properly pressurized, single stage circ.

I was sure to close zones when bleeding and only open one at a time.

I did resolve the problem..Instead of allowing the system to cool down prior to bleeding, I bled the system at operating temperature and for some reason the second floor zone bled normally and is now functioning properly.
I have always believed that it is not a good practice to bleed at operating temperature because of the difference in temperature of the make-up water..Flooding a hot cast system with cold make-up water etc.
Why would bleeding at temp have been effective and bleeding below temp not effective when I bled at the same pressure each time? Odd.
Thank you for your help.
Steve

This post was edited by Harleyfxr on Tue, Jan 6, 15 at 6:04

Most effective bleeding is done at high temperature due to the fluidâÂÂs inability to retain dissolved gases at higher temperatures. This is why I suggested bleeding at operating temperature. Cracking cast iron components is not a great concern as there will be a mixing of the incoming water with existing fluids to temper the thermal shock.

You should have an air removal device between the boiler (air & dirt separator would even be better) and the circulator and another air removal vent at the high point of the vertical riser supplying fluid to zones above the basement.

SR