I'm no expert on vw's by any means , and I don't know what you have tried ,
here's a thought. Might you have an air  bubble in the cooling system? I
have heard about needing to " burp" the cooling system when you do the
bi-annual coolant change. (park it on a 5% grade, run it and refill etc.) My
light was doing the same thing, but when I was working on it there were too
many things going on at the same time! It wasn't running when I bought it!
The other things I can think of would be 1) the coolant to water ratio.  It
sounds like it fires up and runs ok, am I correct? One more thing, try
putting a "full charge" in your battery, take the clamps off and charge it
and put it back in and see what happends! Good luck!