I suppose on tanked water heaters.
My manual says this
To complete the installation of the water heater, you must install
an approved 3
/4 in, maximum 150 PSI pressure relief valve on the
hot water outlet. The water heater has a built-in high temperature
shut off switch, so install a “pressure only“ relief valve. This valve is
not supplied, but is required. The following examples are approved
for use with the water heater:
-
Wilkins P-1000A (Zurn Industries)
-
Conbraco 17-402-04
-
Watts Industries 3L(M7)
-
Cash Acme FWL-2, 3
/4 in
The pressure relief valve should be placed as close to the water
heater as possible. No other valve should be placed between the
pressure relief valve and the water heater.
That's all well a good. Just because the manufacturer states it doesn't mean it passes code.
Plenty of mini split manufacturers state to run their proprietary cable between the outdoor unit and the indoor evaporator head through the building and wall assemblies but will fail inspection because it is not rated for concealed use in wall assemblies as it's not rated as building wire.
If the plumbing codes simply state "follow the manufacturer" then I'm all for following a simple installation manual.
As close as possible as mentioned in mine is a big wide grey area to me. In electrical terms we often consider close as "25ft or within sight".
I'm not trying to argue with you. I know I could just call and play phone tag with my building office on every little detail.
I just want the inspector to show up once and pass it. I feel there is more ahj opinion and preference than code.