by Frank Wild
(Wilmette, IL)
I installed an AO Smith GPHE 50 100 Vertex water heater 3 years ago. I regularly flush the beast; there is little evidence of any precipitate build-up that might cause the house rattling clanking that we get when ever the unit fires-up.
It sounds as if the internals are loose. The house plumbing carries the sound throughout the house---thunk, clank, etc. We got used to the blower sounds after years of a traditional hot water heater; but the clanking is just annoying.