99% sure u need a new thermostat.
simple job, takes about 5 mins to do.
remove the outlet pipe, (maby place a tray under to catch the anti freeze, u'll loose a few pints!)
unbolt the case (3 bolts i think)
simply pull out stat, install new one, and put back together
top up antifreeze.
run it and take it out for a drive
recheck fluid leves and be sure no air locks are present
a thermostat will cost about £15 from Vw, or about £10 from halfords!
Im very cettain its the stat, but if u want to be sure before u buy a new one, then boil some water and put in a clear glass jar.
if its works the stat should click and the diaphram/spring will open
but if its fooked like id imagine then it will do nothing
Also if ur feeling in the mood when u change the stat u can flush out the engine and rad with the hose, and put in new coolant, but again be aware of air locks!!!!
