Window Cleaner caused huge damage to glass.

If you have a business name and address or home address apply to.small claims. It's an easy process. Try to keep a record of all messages and responses ideally written form such as texts.

It will be very difficult to prove unless you have evidence.

It may be repairable

http://glasspolish.ie/glass-scratch-repair/index.html

that may exceed limits of scc

So it’s a rubber squeegee type thing you suspect scraped it? Could you get him to show you all the tools he uses and see if you think any of them could have caused it?

Small Claims Court only applicable in cases where compensation sought is €2k or less.

It's not that much of a mystery. Here's a window glass scraper as described by the OP. Very often the first cleaning of a window will need to remove paint splashes, mortar, silicon/mastic and other stuck-on debris, and a blade when used correctly will take this debris off without damaging the glass. But window technology has moved on and sharp blades aren't compatible with the coatings used on newer windows.

I suppose it's like when we all moved to telfon frying pans and had to drop the metal utensils.

That's pretty clear from the manufacturer's site. It really puts the ball back into the cleaner's court now.

The photos tell the story pretty well too - it was a bladed tool operating in two arcs - top and bottom of the window. I'll guess that the Unger blade had been dropped on one side, hence the scrapes to the glass.

Who was in the house when he cleaned the windows - did they see him use the blade?

Your window does seem badly scratched - Whats baffling me though is why he used the blade all over the window? I would have thought it should only be used on a small area when something hard is stuck to the window. Using a blade all over the window is careless and my opinion window cleaner is responsible ( providing window wasnt in a bad state before cleaning).

Cool the jets. This wasn't a first clean of the glass, as the op said, so again, my question stands. I asked the op if there was any silicone or cement and the answer was no.

As someone who has professionally calened windows in the past I understand how it works.

As such, I can not understand why a window cleaner would ever bring a blade to a window that just needed cleaning. As the op said, he or she had cleaned the glass multiple times before the window cleaner went near the glass.

I would also have serious questions as to why it is just this window that has the scratches. Was the blade used on any other windows and if not why not, if the glass didn't require it...... Just a random thing for a window cleaner to do? For a laugh?

Something not adding up somewhere.

It could end up he said she said and even if you win they might have no means to pay.

What about home insurance for accidental damage?