Re: Heater not working
I had similar symptoms in my Armada, and inbound hose to valve was hot, outbound through bulkhead into passenger compartment was warmish and could be mistaken for hot unless you reach right into bulkhead to feel.
Went to use heat in the cooler months and no hot air, wasn't sure when it stopped working.
Turned out it was airlock somewhere in cooling system. There is probably a documented fix for clearing airlocks from Nissan if you can hunt it down.
To fix for myself, I opened overflow when cold, removed Rad cap, turned inside air controls to full hot, and ran truck.
Added water until overflow bottle was overflowing - in doing so, every now and then the fluid would surge out of main rad cap hole, I just kept going and squeezing top rad hose till overflow was full.
I then caped radiator and let it all come fully up to temp, continued to squeeze hose for a while and checked inside till it blew hot - whole thing took nearly 10 mins.
Once it was blowing hot, I carefully took Rad cap back off and reved gently a few times to expel fluid until overflow dropped back to fill level, sealed everything off with the caps and carefully hosed down all spilt fluid in engine bay.
It didn't take a huge amount of water, and I'm in FL - if you are up north you probably want to pay closer attention to antifreeze level or even top off with pure antifreeze ?
Hope this helps - I was looking at dash strip down and wasn't looking forward to it - Stealership indicated valve was likely the issue ($150 plus labor), but I didn't buy into that as I had previously removed the internal cog and turned manually to no avail, I'm sure they would have been stripping out the dash and printing the invoices for me for a while before they flushed and said they had found it - just my opinion, but they are not called stealership for nothing ;-)
Good Luck !