Makeup water causing boiler failure due to thermal shock

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!

LWCOs are only required on hot water boilers if they have emitters below the boiler in most jurisdictions, if there is no water in the boiler sometimes the aquastat doesn't see the temp of the part near the burner and sometimes gas valves stick on, you combine that with another failure like the pvr is stuck closed or someone keeps the feed to the prv off because they don't want a flood if a hydronic pipe breaks and suddenly you have a dry fire event. The same sort of things can happen with a warm air furnace.

analysis paralysis😯

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.

there was like a 10 page discussion on hartford loops that I didn't read but the main upshot is that it is largely leftover from solid fuel fired boilers where stopping the fire is difficult to do quickly if the water runs out of the boiler.

No.