This was a first for me.
The water heater has the normal TPR installed on the side of the unit.
Then on the top of the unit there is a TPR valve installed on the hot water line to the home?
Is this a home owner install? seems like over kill to me.
Any thought on this 
Hmmm need to think about that one.
Replacement (DIY) for a bladder(expansion) tank ?
Bob,
You are all over it. As current codes require a device for controlling thermal expansion of the water supply and can not utilize the TPRV of the heater “Harry Homeowner” attempted to comply, but installed on the hot water out instead of the water supply side
