I found this to be an excellent guide to Aqua/Hydra Hot servicing and maintenance. It's on a Allegro focused site but what the heck. Good write up, easy to understand instructions, and pictures!
Tim, you might want to provide a link on the member center. I did a search and didn't see any previous mention of this on the forum.
http://www.rvcruzer.com/aquahot.phpSteve
