No Heater, except when driving fast!

My car also did this. Check the coolant levels in your radiator and the reservoir. My levels were low and once I filled them back up, the heater worked just fine.

And what about if your coolant levels are good and it still doesn't work

I’m with Ro! Earlier this winter I had a problem where my 2006 Altima 2.5S would only blow cold when at an idle. Upon driving, even at low speeds, the heat worked fine. Today it decided to quit blowing warm air except when driving at highway speed. All fluid levels are good.

Weak water pump and or bad sticky thermostat

Air pockets in your cooling system is the cause.

Okay so there are multiple issues, But we have seen people replace water pumps , bled the system and replaced thermostats FOREVER .. Not the problem 2005 Nissan Altima .. the fix? Reverse flush of the heater core netted a level of gunk that was an afront to god. and this was a car well maintained into 100k with system flushes . These heater cores are junk, or they collect junk from the system because of their position in the car (too high) there is some dynamic here and unless you are losing coolant without any sign of where it is going , It is probly nto a head gasket.