Where is the water going

SBoston

So I have a question about the water line in my boiler. As a habit I check the water level every week or two to make sure that I don't need to add water. The Burnham IN6 boiler was installed about 2 years ago. I noticed that every few days it seems that the water level is dropping. I checked to make sure that there are no leaks when the system gets up to pressure, but other then the standard clicking and breathing of the vents I don't hear/see anything. Just to make sure I also checked to see if there was any steam coming out the chimney, but there is nothing. About 4 years ago we replace the wet returns so I know it's not them leaking.



The other day I added a little water to the boiler and after a short fire and cool down I noticed that there was more water in the boiler then when it started. So the added water came from somewhere.



Could this be a problem with water getting back into the boiler from the returns? Or is adding water every 2 weeks common place even in a new boiler.