Stuck drain valve.
A drain valve on my hydronic heating boiler is completely stuck. The valve does not have a bonnet, the stem seats in a valve body. A gland nut covered some kind of a packing which was like rubber and crumbled easy. The handle end of the stem is broken off. The valve leaks slowly, only a bit faster than evaporation. When I discovered the leak the valve was encrusted with calcium deposit end rust already eaten through the metal wall. I tried to use big wise grip and 12” pipe wrench on the stem without any success. I suspect that even when I unscrew the stem it will be unusable. One reason is broken off handle. To replace the whole valve I’m afraid to do something to thread in cast iron body of the boiler. The valve is installed using some kind of plumber putty that is now hard as a rock. Any advice how to approach this problem? Another question would be how to drain water from the boiler when the drain valve is unoperative?
That looks like a water heater not a boiler. If it is a water heater it's time to replace it.
It is Peerless boiler made probably in 1960 (serial number starts with 60-...), 160k BTU, still going strong, cast iron body.
IT is a brass valve into a cast iron boiler. You will NOT do anything to the boiler when you remove the valve using a BIGGER wrench. Turn off the water to the boiler, close the valve to the expansion tank, open the relief/safety valve to remove the pressure, then close it so no air gets into the system. Remove the drain valve and QUICKLY screw the new one in with minimal water leakage.