If it's a new screen needed check your insurance policy - some insurers limit their cover on a new replacement screen to a value of £400 or £500. My new B Max screen (under extended warrantee thankfully) was over £1000.
I needed my screen changing not that long after I bought it., so it didn't cost me anything.
I'm convinced dealers sell cars with known faults, knowing they will be fixed under
warranty, so not costing them anything.
I has a similar issue. Found a work-around. Try this befoe going to any expense.
1, turn fan dial to full
2, turn heater dial to full till is engages air con (yellow light next to dial)
3, Only at that point press the heated windscreen
I can only say it worked for me. If I try any other sequence then nothing on the drivers side.