hot water baseboard

hello i have a gas boiler with four zone with separate
circulator pumps three zones work fine but the one
for the basement keeps getting air in it it will be fine
for a few days then air will get trapped and the
circulator pump will run without pumping any water
each time this happened i bled some water off thru
the valve for that zone and everything is fine for a few more days then it happen again. thanks for any ideas
on this. dylan

 

1st hydronic heating is not my niche in the market, but as no one has offered ideas I will offer my thoughts. 1. Has the system compression tank been checked for a faulty diaphragm. 2. Are there automatic air eliminators that could be malfunctioning. If not a tech should be able to add an automatic air eliminator that wil bleed off any accumulated air as it is encountered.

 

I am assuming that you have already checked for leaks in that run. What is the water psi? You may be water bound and not air bound if the psi is above 15psi. Also try boilerroom.com they may have some ideas.

 

mark thanks for your reply yes the system does have
an expansion tank i guess it has a diaphram it does have an air valve on top similar to an auto tire what should the pressure be? also the problem zone also has an automatic
air bleeder with a tire valve on top if i push the pin some air comes out and then water. is it supposed to let the air out
automatically i dont see how it could.


fjrachel thanks for your reply your right there are no leaks
i dont know the psi how can i determine it ? also i dont know what you mean by water bound not air bound
please explain thanks dylan

 

As water is heated, it expands, this requires additional space in a closed system. the compression(expansion) tank has h2o in the lower portion and air in the upper area this allows the air to be compressed to make room for the expanded water as this is locatedat a system high point it is also a good place to collect air that has entered the closed system so it can be bled off. The bleed off with the tire type valve is a collection point but is a manual bleed an automatic bleed will have an openng in top & a float arrangement internally to automatically vent accumulated air. The centrifugal pumps used in this type of application are "non-positive displacement" type which basically means if the pump body is empty it can't "suck", only by pushing the fluid out of the pump body do we have a reduced pressure area to draw in additional fluid, so if pump has a lot of air in it it "loses prime." When a pump becomes "water bound" it simply means that the pressure differential between inlet & outlet is greater than the pumps ability to impart enough force to the water to overcome the outlet pressure, so flow ceases.--Mark