Heated rear screen issue

[wideboy666]

My heated rear screen doesn't work as it should...

Press the button and the switch lights up and you hear the relay click, the mirrors get warm straight away, but even after it has been on for 20 mins it has only cleared a couple of mm at each side of the elements...

VW stealers claimed that it was a faulty screen and the only solution was a replacement screen. And the local Indy said he had known of one where the screen was faulty..... So today took out the rear interior panels disconnected the live end of the screen and ran a 12v feed direct from battery to the screen and hey presto the screen cleared, so it would appear the the screen itself is okay, I then tested the voltage at the terminal leading to the screen and was getting 0.05 volts.....

So where do I head now with this, any ideas?