I needed to replace my thermostat as the temperature gauge didn't ever get passed 80 deg and most of the time sat near to 70-75 deg I had already replaced the coolant temperature sensor the week before and that made no difference so the next step was the thermostat.
I was also replacing the radiator at the same time but I haven't bothered with that as their are loads of write ups for removing that.
First of all I popped the front bumper panel out by squeezing the top and bottom fins and a good tug it should come away, then connect a pipe with 1/2" internal size to the drain on the radiator and undo the drain screw just in front of where the pipe fits.
I then disconnected the battery
after doing this once the header tank was drained I removed the header tank as this was being replaced with a nice new one too, then I removed the large throttle body to intercooler pipe followed by the complete throttle body without disconnecting the wiring this can then be rested on the engine mount below
(I didn't disconnect the throttle body wiring as you need to do a throttle body adaption with full registered version of VAG COM if you do) YOU HAVE BEEN WARNED!!
I then disconnected the wiring from the alternator as it's slightly in the way
once you have removed all this you should have a clear view of the thermostat housing like this, this was actually after fitting my new one (hence the small amount of coolant) but you get the idea
undo the 2 bolts holding the housing to the engine block 5mm allen key or 10mm socket, I found the allen key on the lower bolt was a little tight and started to round so undid with a socket instead, the lower bolt is a little tight to get out as you cannot get your fingers down there too but once you've cracked it off it comes out easily leave the last couple of turns and you can use the housing to hold the bolt and stop it from falling down.
once you have removed these you can move the housing out of the way and you are left with this
just remove the O'ring and then you can remove the thermostat
installation is as they say the opposite of removal
after fitting the thermostat I then fitted my new header tank and refilled the system
then gave the system a good bleed out of any air, people say you need to disconnect the pipe next to the battery but I've never needed too just put the fan on full inside the car on full heat
once the system is up to temperature I gave the area a good wipe over
that's it job done
enjoy and now my car runs dead on 90 deg again
Hope this helps someone in the future, all in all inc changing the radiator the job took me around 2 & 1/2 hours inc lots of coffee
