I have old circa 1930s/40s? Baseboard radiators that always seem to be full of air.
I bleed them at the valves and it is OK, but it only lasts for a day or so, and then the darn things are cold and I have to bleed them again, what's up? Sometimes when I bleed them only cold water comes out and it seems like no pressure in the system. I just shut the valve and pretend that it is OK and usually it is?

I think I have some problems with my well system and my pressure tank not functioning properly. I was wondering if that might somehow be letting air into the system?

I don't seem to have any leaks, at least not where I can see any evidence of them, on the floors, plaster, etc. How else to do you check? Pressure test?

Anybody have any experience using a Rannai instant hor water heater as a boiler? I just put one in for the upstairs bath and it is pretty slick. I see in their catalog that they can be used in that capacity but I would like to make sure before I take the plunge.

You have a leak in the system and/or the pressure reducing valve is not letting in water.

Thanks Northernheat for your reply. I just had the pressure valve replaced which may solve the problem, if not, how do I test for leaks?

The easiest way is to turn the valve off just before the reducing valve and see how long the boiler pressure gauge holds water. Most systems are easy to find water leaks unless it is in the slab, then it gets more difficult.