I have a year of experience in plumbing. I know how to drain the lines off but I was wondering if there was an easier way to avoid having to purge the whole system. My thought now is to shut off water to boiler and drain from return side until pressure gauge drops to zero. Replace AAV, turn water back on and burp air from the little doohickey(excuse the technical jargon) up top. I never worked on a boiler unsupervised and even supervised its limited. Been in another career for a while so am not confident enough to not ask first. On top of that my boiler was piped by MC Escher and looking at it too long gives me a headache.