At my current house I have one expansion tank on my water heater, and another on the boiler system piping for my radiant heat. I'd like to replace them when they get "old," but I don't know how to read the date codes on the tanks. I've Googled this subject with no luck, so I thought I'd try here. For example, the date code on the radiant heating system is: 14121501. Does anyone know how to decipher this?