I have purchased a new water heater to replace the original 11 year unit. I am concerned in attaching the existing fittings to the new unit. I believe the builder used pex directly to the original heater. What is unclear to me is how these will behave when I begin to unscrew them. Should the fitting (B) slide free of the cold side brass fitting (C) or must these pieces be replaced? I believe the black fitting (E) will rotate free, but I have the same concern with the connection to the pressure valve (F) as I do the cold water supply.
PEX pipe won't slide off the fittings if spun because they are on there through compression and not screwed on. I've spun the crimp style fittings without issues but never spun the style you have before but from what I've read, you can spin them with out issue. If you decide to cut the pipe, remember you'll need a spreading tool to reconnect the pipes or use something like SharkBite fittings. You can reuse the brass fittings by cutting the ring with a knife and then heating up the plastic pipe and then bend it back and forth until it comes off. From what I've read, you can do the same with the plastic fittings but be very careful not to cut or overheat them. I'd just replace the plastic ones instead.