I have a 5 year old AO Smith gas water heater and after I flushed it out the drain valve broke. I bought a replacement but after shutting off the water supply it would not drain. Is there something else I need to do to drain it?
You need to allow air into the tank. Preferably by raising the lever on the safety relief valve at the top of the tank. After you are done, the relief valve may leak if it was time for it to be changed.