Yes getting air out of the coolant lines can sometimes help. And the heater hose valve at the firewall is the place to do it. But if you have a bad thermostat or blocked heater core then it won't really help. On my 2000 v6 Passat a coolant flushing helped for a while. But then it became clear that the thermostat was the likely problem, And that's a big job, Basically a timing belt/waterpump job.
SOURCE: 2001 VW Passat
Ok, have your coolind system backflushed. Your heater core could be clogged. This could have been caused in using the wrong antifreeze system or mixing the green with the vw g-12 antifreeze. This could ran you about $110 to 150 dollars at a radiator shop...stay away from the Jidffy lube or oil doctor's . This could be your cheaper alternative to solution to your problem..good luck..
SOURCE: Low heat from my 2001 Passat heater
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.
SOURCE: 2000 Vw passat,had no heat.
The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow. If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm. If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air. If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted. One or a combination of these factors is likely the culprit in your case.
To attempt to clean the core, you must flush the system multiple times. If it is still problematic, changing it is your only remaining option besides the water pump itself.
SOURCE: The heater on my 2002 VW Passat is blowing cold.
I have the same problem, but mine was because someone put stop leak in it! otherwise, check my profile, someone posted a answer that may help you.
SOURCE: my heat not workini but blow cold air where is
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.
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