Having heat problem In my 2002 nissan can you hook up a 12v pump to increase coolent flow up in heater coar

Didn't mention that your car is overheating, so I will assume that your coolent is FULL and your waterpump and thermostat are working correctly, and that your car does get to normal operating temp (around 180-220 degrees F).. If the above is true, then disconnect the heater hoses from the engine and see if its clogged up with rust and/or corrosion. This spot is famous to get gummed up, restricting coolent flow through your heatercoil.

Assuming that you have the proper amount of coolent added, check where your heater hoses connect to the engine block for rust and corrossion, this is a common area to clog up, preventing coolent flow from circulating through your heater core. If ok, check for a thermostat that is stuck open.

Did you change the thermostat? It could be stuck in the open positon, or in backwards, or missing all together. I would like for you to check your heater hoses where they connect to the engine, as this is a very good place for corrosion to build up, restricting coolent flow to your heater core. If this don't fix your heat, I would like to know the reason you changed the water pump. Was it overheating? Did you have heat before you changed the water pump?

is the radiator full of good coolent is heater hoses hot if not the water pump may be bad if the hoses warm the problem in side the h vac system

Heater core may be clogged. Try flushing it to see if water flows through freely. Also check the heater water control valve for restrictions.

disconnect the pipes that feed the heater and join them together with a piece of copper pipe

I'm having the same problem, no heat at idle. I replaced the waterpump/both thermostats/belt and radiator. I'm still having the same problem. any ideas?

Thanks,

Kurt

do you have a "check engine" light on? A bad temp sensor would give a wrong reading. Do you get heat from your heater core? Also make sure you are getting a good flow from catalytic converter and muffler so you know they aren't plugged heating up engine temp. Also make sure all your heat shields are in tact. Are you using 50/50 mix or mostly water? Though in cold temps you normally want to use more antifreeze less water, I would try more water, less antifrezze.

Check and see if the Thermastat is stuck closed.

I live in Alaska and have had the same problem i just added more coolent to the radiator and it warmed up i installed a block heater and i leaked a bit and the coolent level got low and i would have no heat. I tryed to fill just the coolent resivoir and that dident work so i filled the radiator pumb full and that worked!! Hope this helps.