Rear heated screen only half working

[rj1986]

So this is a bit of a head scratcher-

Got into the car last night, whipped on the rear demister as per usual.
About 5-10 mins later, i noticed the top half was crsyal clear, but the lower half was only clearing around the elements but not inbetween them.

So i checked to make sure the boot was fully closed (it was) and decided to go to bed.

This morning i whip it back on and no change. The top half of the screen is almost hot to the touch, but the lower half is luke warm at best.

Any ideas?

It's half working so it's not fuse related. Is there a relay that controls separate portions of the the screen?

[X5Sport]

Check all of the elements for gaps.  I had the rear screen heater in the X6 delaminate when it was a year old.  That meant a new screen.

You can get silver loaded paint to repair breaks.

[rj1986]

Wouldn't a gap mean no heat at all?

[grumpywurzel]

No mate, a small gap will cut off the current flow to that part of the screen. It's common to have one line of the heater fail if damaged. If you have lost around half a screen have a good look at the element on the outer edges

[X5Sport]

Running a car circuit tester carefully along each element to see when the light goes out will also find a break.

Volts are fed in on one side, run through each element and ground the other side.

A crack on any element stops that one only but losing a load sounds like a side break as suggested above.