I'd look at the head gasket.
Coolant pressure doesn't build up straight away, and a lack of heater function generally means something's awry in the cooling system - usually a blown head gasket or cracked head.
There are solutions.
Cheap - Chemweld/Liquid Copper
Pros:
- cheap
- fast
- may point to the leak (particularly Liquid Copper)
Cons:
- may not last forever
Mid-range Expensive - eBay preassembled head
Pros:
- cheaper, at about $1200 without fitting costs
- fully assembled with valves and camchains all shimmed and ready
- usually come with full gasket kit so installation is easy
Cons:
- It's not a genuine head and may be of inferior quality (see * below)
- Warranty is an unknown, they say it does have one but I've not tried it
Expensive - Genuine Nissan Parts
Pros:
- It's going to be correct, 100% and no need to fear about it at all
- It's going to work like new
- Nissan warranty will be guaranteed
Cons:
- Expensive. Nissan know you need it and extract $$ accordingly
- Their service droid does the work, not necessarily an experienced mechanic
* Note: I've had my head replaced. Got a cheapy off eBay. Mechanic who did the installation said it was perfect, had all but one gasket and that was easy to source. I've put about 20,000km on it since and it's been perfect. Almost better than new. Mine was $1200 delivered, about $2500 to fit (including disassembly, plus new water pump and new thermostat).
