Heated Rear Window Playing Up

[Parker]

Advise please, the top half of my heated rear window stopped working, the fault was easily found wire broken from solder on the window. I reconnected and it worked fine then it stopped again just a few days later, made sure connection was ok and again fine and then once again stopped working. This has happened about 6 times now. The contacts are good and clean but now I can't get the top half of the screen to clear just the bottom. Any ideas? Is there a fuse that will affect the top half only?

The air blowers do clear the window but it's one of the niggling things that should be working fine.