Do I have to replace my expansion tank, or can it be drained?
I have a gas hot water base board system with an expansion tank. The tank has a drain valve to which I can attach a garden hose. I drain the tank at the beginning of the heating system and check it on occasion. If the gas boiler pressure rises quickly then the expansion tank probably needs draining. I may drain mine once over the winter. I don't understand why your expansion tank does not have a means of draining but if it is fairly good condition I think it would be much easier to install one than replace the tank. If you go with replacement get one with a way to drain it.