I have a three zoned forced hot water baseboard heating system. The basement and 1st floor zones are woking fine but the top floor does not produce heat (this season only). The thermostat has been tested and works fine. When I call for heat, I can hear the pump humming, but i’m not sure if it is pushing water through. Could it be an air block? Any help out there? Thanks in advance. Jack
It can be an air block. Check the pressure on the boiler gauge. The pressure should read at least 1/2 the number of pounds on the gauge that the top radiation is in feet of height from the boiler. The top floor is also a likely place for air to cause a block, as bubbles rise to the top of water.