Hey Everyone (and Tom!)

Okay, new house to my wife and I... we've had it less than a month and two days ago it was time to turn the heat on. This is an old hot water system, no pump (works by gravity) in a three story house.

The radiator in the master bathroom wasn't full, so I tried to bleed it. Just a little air came out, and it didn't fill. The bottom half of the radiator was warm so the radiator shutoff isn't stuck closed. Off to the basement I went. The auto-refill on the system comes from the main water line, is "stepped down" to 12psi through a reducer and then has a 30psi relief valve going directly to a drain. I have two boilers run in parallel (one coal - unused, one gas), and each has an "Altitude" gauge on it with no units listed (is it psi or 'feet' of water?). They both have red needles set at "25", and had black needles (the actual measuring ones, and neither are stuck) reading at "25" on the gas and "20" on the coal. These things are 75 years old or so, so I don't expect them to be 100% accurate.

Anyhow, I pulled a little handle on the 12 psi "step down", hoping that it would help me auto-refill (I have no idea if the handle is lets the water pressure get to 12 psi or if it bypasses the 12psi and lets the full "line" water pressure through). My wife sat upstairs bleeding the radiator. Pressure gauges on the boilers go up, 2nd floor radiator is bled. Yay.

On to the 3rd floor. All of these radiators are almost empty. They all have brand new valves on them, so I guess they were drained for the valve installation. Unfortunately, the guy who owned the place before us passed away, so I couldn't even ask him. So, same thing as before, I pull the handle on the pressure reducer, wife bleeds the radiators. Well, this time I stop early and say "uncle". The altitude gauges on the boilers read "32" and "27", and I decide to call it a night before I screw something up.

I know that it should only take about 15psi to fill up the water system (guess that the top of the topmost radiator is 35' (max) above the pressure gauges... 35'/(28"/psi)-> 15psi). Sooo... what's going on? Are my "altitude" gauges on my boilers measuring "vertical feet of water" or psi? Am in endangering my system/boilers by pulling that handle on the pressure step down in an attempt to fill my radiators?

Actually, I guess the real question is: These " or psi? Am in endangering my system/boilers by pulling that handle on the pressure step down in an attempt to fill my radiators?

Actually, I guess the real question is: These " gauges have no units listed on them. Is it normal for these gauges to measure "height of water column" or is it typically psi?

Thanks in advance!!