No Heat My 2006 LaCrosse is not giving out any heat. I have replaced the heater core, the water pump, and the thermostat. It always seems to work until the next time the car is started. It was taken to a radiator shop today, and the radiator was flushed in case there was an air bubble. It worked - until I started it 2 hours later. It was blowing COLD air - colder than the outside air, so I assume it was the AC (even though it was set to 90 degrees). Why would it work for a minute every time someone works on it, then not work when I start it? (I know I'm cursed, but I doubt I need a witch doctor for my car.)

There are several possible reasons why you may be experiencing cool or no heat in your 2002 Jeep Grand Cherokee Laredo after replacing the thermostat and bleeding the air out of the lines. Some possible causes could include:

1. A malfunctioning blend door or actuator: The blend door controls the mix of hot and cold air that is directed through the heating system. If the blend door or actuator is not functioning properly, it may cause a lack of heat.
2. A clogged heater core: The heater core is responsible for transferring heat from the engine to the cabin of the vehicle. If the heater core is clogged, it may not be able to transfer heat effectively, resulting in cool or no heat.
3. A faulty thermostat: If the thermostat was not properly installed or is not functioning correctly, it may cause the heating system to not work properly.
4. A problem with the water pump: The water pump is responsible for circulating coolant through the engine and heating system. If the water pump is not functioning properly, it may cause a lack of heat.

Heater core is plugged more than you can clean

Last step is to flush the heater core. After that, replace the heater core. You need a manual, because you have to remove the dash.

heater hoses run from the rear of the block to the water pump. One hose into the heater should be hotter than the other because heat is transferred in the heater in the car. . The cooling system draws water from the bottom of the radiator ( water pump inlet)which is always cooler than the top hose and dispenses it throughout the engine and heads including the heater core. It is then pushed past the thermostat with all the heat from the engine to the top of the radiator where it is cooled down by the air passing through the radiator . Check that the air vent for the cabin is set to recirculated cabin air and not fresh air from the outside as it will require recirculated air to increase in temperature to work properly

THIS IS A JOB FOR AN EXPERIENCED MECH. TAKE IT TO A MECHANIC WHO DOES SIDE WORK.

heater core clog,water pump.

I would think at some point in the vehicles time life some one has added a stop leak(bars, penzoil) or pepper to plug some kind of leak. Doing a flush won't always clean system out and yes your heater core is plugged giving no heat. Unfortunately its not an easy replacement as the other post is correct, complete removal of dash to get to heater core assembly.

You may have loosened or lost some material into the system while changing the pump and caused a blockage in the heater core. There could be a little coolant going through to warm up but not enough to continue supplying heat once the initial heat is drawn down.
Ideally a back flush through the heater core may take care of it. You should be able to find a kit to help with in an auto parts store.
Open the hood and look on the firewall of the car. There should be 2 rubber hoses going into the firewall and into the car. They will likely have spring clamps just like on the radiator hose. Remove both lines. Then get a hose and put it in one line and run the water until it comes out clear. Then do the same thing with the other side. Do this a couple of times. Then reconnect the 2 hoses ahd check the level of the radiator. Then start the car with the radiator cap off and wait a while for the thermostat to open and have the heater on so it will cycle through the whole system. Then top off as needed.

Is the thermostat in correctly?

sounds like another plastic rad has bitten the dust,replace the rad or hose if its split and refill with antifreeze and see what happens ,if ok then good if not post here again for more advice