Audi a4 b6 1.8t overheating issue NEED HELP!
 

The reason this problem started was because i was driving on highway and i went to 19psi , out of no where coolant sign came on / overheating needle went almost to H . and i took the exit went to gas station looked at my coolant it was full , so i let it cool down and then drove it home slowly . next day it's not really bad over heating but when ever I start my car and let it warm up , so far it's good . The needle goes right in the middle and stays , so i keep driving and about 10-15min later, the needle goes above middle and I can hear the fans being on . It doesn't keep going up but it actually fixes it self and goes back to normal. But sometimes it stays between the middle line and the next line . I don't let it reach Hot . So I turn the heat to full blast . I also had my water pump done 28k miles ago with the timing belt and tensioner . Also I did coolant flush today. I'm not sure what the problem is , is it thermostat ? Also I tried if I keep heat on full blast the car goes back to normal temp and it will sometime raise up and then come back to normal after a min. I'm not sure what the problem is.

This could be a thermostat stuck in the closed position, thus preventing free flowing coolant. Was this changed with the timing belt?

Also, are you noticing this overheating condition before or after the coolant flush? If after, did you bleed the coolant system in order to get out any air pockets?