How do I replace the expansion tank in case of failure?

The boiler will first need to be drained. The electrical circuit(s) will need to be powered off in the electrical panel and then disconnected from the boiler. Consequently the low voltage circuits need to be removed as well. Then remove pressure and drain accordingly to remove the boiler from the wall. An option method for removal is to remove the expansion tank holding bracket. There are two screws located on each side of the boiler. The pipe connections will first need to be removed in order to slide the tank down from the back of the boiler.