2004 volkswagen passat v6 no heat

Sounds like either low anti freeze, thermostat is not working or your heater core is leaking. Is there any anti freeze leaking under the car? You water pump could be bad if there is fluid on the ground below.

Could try to change temperature sensor (due to MIL light), but it doesn't cause no heat in vehicle. Most likely caused by air-lock in heater hoses at heater core. Try bleeding hoses to eliminate air.

Your heater core could be bad.

sounds like the raditor is not full.
fill it and let it run with cap off after it get warm look and see if it went down and add more water or antifreeze to get it full.
other wise it could be clogged and you will need to back flush it.

we have a 2004 passat with the same problem. after many different attempts. what we did was. drain the heater core, blow air through the system and then put a mild solvent in the system and let it set for about 20 minutes. flush the system and refill with coolant. now our heater burns us out. use low air pressure and be very carefull. heater core was full of junk that came out after we flushed with solvent.

any help no heat 2005 passat changed heater core i get warm air with nothing on as soon as i turn on the heat the a/c comes on

Has the car been changed coolant since it was bought? If it is time to change, let do a flush through a heater core. There are 2 coolant hoses going thru a fire wall. One for coolant in and one for coolant out. Heater only works if coolant is flowing through the heater core. Therefore, there are one or both following cases contributes to the problem: 1-If the valve control coolant flow gets stuck, then it always closes  so there is no heat. 2-If the valve is working, but the heater core gets clogged up, then there is no heat.

I had the same problem and remedied it by disconnecting the heater core at the firewall (you have to remove the plastic shield by the windshield to access) and filling the core with radiator flush. I let it sit for 4-5 hours and then flushed the core with water from my garden hose. To make the connection, I cut a rubber washing machine supply hose, which fit inside the tubes to the heater core.

Once flushed, I added "Water Wetter" to remove any air bubbles from the system. heat now works great.

BTW - both the dealer and and independent said I needed to replace the heater core, at a cost of $1500. Glad I tried this first! Good luck!

There are known problems with this vehicle's heater core not getting enough coolant flowing through it to blow hot air.
1) Even if the coolant looks good, there are problems with the heater core plugging up. One solution is to use a heavy duty cleaner (CLR pipe cleaner) to back flush the heater core. To know if the heater core is plugged up, disconnect the 2 heater hoses at the heater core and somehow connect a hose to one end of the core. Try to flow water through, it doesn't have to be high pressure, and there should be a steady stream. If not, try to get the cleaner directly into the heater core and let it soak. Then back flush it and a lot of scale should be seen coming out.

2) The other problem is that since the heater core is the highest point in the cooling system air tends to get trapped in it. This should only happen if the coolant goes low or someone has opened the system to service it. There are a number of ways to bleed the system (vacuum bleed, pressure bleed). One of the hoses should have a small hole in it for bleeding air, pull that hose back just enough so the hole allows coolant to flow out of it. Then accelerate the engine and get a good flow coming out, when no more air bubbles are present, there should be good heat.

3)I've heard of bad water pumps with low flow causing issues as well as an aux. water pump not fuctioning correctly leading to poor heat output from the heater core. Someone should confirm this as I cannot get much information on the aux water pump(electronic pump by the alternator that is supposed to run after the car is shut off).

Hope this helps.

Had this problem after replacing water pump. Hard system to bleed. small bleeders on heater hoses and one near the front of the engine.
VW vortex has a post on cooling system bleeding. check to see if both heater hoses are hot. if so check the climate control: push econ and mode at the same time. it will give you codes. The blend door can be checked for freedom of movement.