The return lines are clogged
If you have an automatic feeder and any buried steam or condensate lines, it pays to install an inexpensive water meter on the feed line. Keep a log of how much water enters the system. It's normal for all open steam systems to take on a some water, but if you see the meter reading suddenly jump, you know you have a leak. Find it and repair it.
If you flush returns regularly, they'll be less likely to clog.
To flush the lines, close the gate valve, and fire the boiler. When you build up some pressure, open the ball valve. The steam will push the crud out of the system. You'll have to feed the boiler while you're doing this, of course, because the condensate won't be returning from the system. This method works especially well when you're trying to clean a new boiler.
All steam systems need to be flushed regularly.
If you use a dry return, steam might have access to those drip lines. It will flow up the riser as condensate tries to fall down. That can cause water hammer. It's possible to run a dry return, but you'll have to use loop seals between the riser drip and the dry return. Go ahead and raise your return line, but connect your riser drips from their present location at the floor into your new dry return. What you'll wind up with will be loop seals. A loop seal is a U-tube that fills with water and keeps the steam from working its way up into the riser drips.