Thanks Gary, 
I understand the purpose of the bypass valve. I'm just not comfortable with the idea of having to open the bypass valve to prevent the heat exchanger from going nuclear.  I work alone and have to put the wand down for longer periods of time than a 2 man crew would have to.  That's why I like my fuel fired system.  
My understanding is Amtex systems don't have a diverter valve?  I hope to someday upgrade to a larger system (probably a heat exchanger and get a part time helper) but I would set it up so any hot water would be bypassed back to a water box or fresh water tank rather than waste tank then have to remember to crack open and valve on my wand.
 
The Amtex looks like a good little machine and makes some pretty good hot water, but I just don't trust my memory that much.  
