Car is still at the dealership (since Tuesday morning). They told me
that the heater core was airlocked and they had drained the coolant,
purged and replaced it and thought it was fixed but when they tested it,
no heat again. Repeated the purging process without success. Still no
heat.

The service manager told me they have a call in to Nissan for assistance
in finding the problem.

I am going to go there later this morning and let them know what the
problem is.

When I picked up the car last Saturday evening and drove it home I
noticed a slight electrical burning odor coming from the engine
compartment. I noticed it again on Sunday but then it went away.
Didn't smell it again.

I informed the service manager of the odor when I brought it in on
Tuesday but they sorta brushed it off saying the car was new and it was
probably just things getting hot for the first time.

Maybe, but I know the difference between a new "hot" odor and an
electrical burning odor.

Anyway, after doing some Google "research" I discovered that there is a
motor driven coolant control valve in the engine compartment, mounted on
the firewall. When the climate control calls for heat, the motor opens
the valve, allowing coolant to flow through the heater core. When no
heat is called for or air conditioning is being used, it closes.

I think the valve was stuck or jammed shut from the factory. When the
little motor tried to open it, it first overheated and eventually burnt
out which accounts for the electrical burning odor that then went away.
It also accounts for no heat, obviously.

Need to be diplomatic though. Sometimes you can **** people off by
trying to be helpful, especially when *they* are supposed to be the experts.