Steam Boiler Shutdown for Summer

If It Was...

...my steam boiler, I'd drain it, flush it out with a hose, and leave it empty and open for the summer. I'd even break the union after the make up water feeder to make sure the boiler stayed empty. Filling it with water DOES work. But you need to check it periodically to make sure it stays full. Leaking blow down or drain valves will let the water level drop. This upper layer of water will absorb oxygen from the atmosphere, and pit your boiler at the water line. You should likely check the level once a week. Everybody starts out with good intentions, but are you REALLY gonna do this all summer? Drain it and leave the valves open, plugs out, etc. Nothing to look after now.

When you refill it for next heating season, fire it up right away. You don't have to crank it up to overheat your house, just fire it long enough to make some steam. This will drive the dissolved oxygen out of the fill water, and minimize corrosion.