I own a house that has an apartment next to it (side-by-side duplex). Recently the tenant passed away. All the utilities were turned off including the water. What happened was it seems water filled one of the radiators and then froze. It burst a piece of cast iron right off! I remove the radiator and took it out to be welded, but I noticed that one of the pipes still leaked. I put end caps on both pipes and then, when I re-installed the radiator and removed one of the end caps it spewed water everywhere for about 5 sec. and stopped. Why is there water leaking in this system when all utilities are turned off?