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I do this on every steam boiler that I am service. Just for clarity, I only service residential. Cleaning is part of maintenance. The eight way will break down the sludge. Repeated draining remove the sludge. Adding eight way after the fact, will greatly reduce the sludge going forward.

@ethicalpaul - I don't actually know. This was before I got interested in home heating, it was a poorly maintained rental, and I was vaguely recalling that's what the plumber told us (over a decade ago). I think we just came home from work and noticed the house wasn't heating. I don't recall the basement flooding in the same incident.

So all of the fear with Hartford loops etc on steam boilers yet hot water doesn't have it and doesn't even have a lwco?

Well water leaks will cause the system to use more water but that is about it in the short term. I believe you have other issues that need attention too.

If anything I'm amazed at all the comments about dry fired boilers.

1. A house I was renting had a steam boiler crack. The LWCO was broken, the boiler steamed itself dry, and then returning condensate caused it to crack when it met the red-hot boiler.
2. As part of my on-going experiments in improving (hydronic) boiler efficiency, I've settled on a scheme that immediately opens all of the zones in the house to do a 'thermal purge' cycle when the last zone is done calling for heat. This effectively means dumping a lot of cold water into a hot CI boiler, and it can drop the temperature from (up to) 180F down to 65F or so in a few minutes. I haven't noticed any detrimental side effects though, and the temperature change seems pretty gradual, as the cold water is mixing with the last-active hot water loop (plus the water + thermal mass of the boiler itself).

I'll definitely report back if I crack my boiler in half this winter!

For what it's worth.... Part of my regular maintenance, is to put 8-way into the boiler. Fire boiler until it steams. Shut off. Fire on and off to keep boiler hot. For approx half hour. Drain boiler completely down. Fill, with manual valve. Full speed. Until boiler is full. With cold water. Drain and fill, drain and fill...until water is clean. Fill back up and fire.