When all else has failed, I have had success in the past with these type of screws by removing the head with a short sharp tap from a small cold chisel. They are typically fairly soft as far as fasteners go. You can then wind the remaining thread out the underside.

If you are not confident with hitting things delicately, probably should be a last resort :)

Sharp chisel to take the tails off, then punch screw upwards?  Even gentle levering might them pop the screws.

Presumably new fan plate will be secured using hex-head nut and bolts for next time? 😄

Ge0rge: How is it attached to the wall? Have you considered taking it down, doing the job without resorting to hammers, and then remounting it?

Great thinking - outside the box. 😁

Thanks, I could chisel one side, or two sides but because of where the cabinet is unfortunately I couldn't chisel opposite sides.

The right angle adapter is an interesting one, we've got several items in the Ryobi 18V ONE+ range but it seems their right angle drill is a poor design because the battery end doesn't rotate. I have a brushless drill driver instead of an impact driver though, it seems the right angled adapters all specify they're for impact drivers?

Good question about taking down the cabinet. It's an 18RU 600mm cabinet bolted (4 bolts) by the builders into extra blocking placed inside the wall. It'd be possible for a few strong people to remove together but something we'd really prefer not to try since there's such an easy work around to the heat problem (remove the cabinet door).

Long nose vice grips should easily be able to grip and lock on to the side of the screw head and rotate it.

https://www.supercheapauto.co.nz/p/toolpro-toolpro-locking-pliers-long-nose-160mm/540523.html#q=vice%2Bgrips&lang=en_NZ

Um, what about cutting a piece off the top part of the glass and use a fan placed at the bottom of the cabinet that would force warm air out through the gap at the top??

Open ceiling hatch, climb into roof space, Jigsaw square directly above cabinet .... simples 😉

Keen to hear a good outcome with this.

My thoughts are basically the same as others:

- Spend the time and take the cabinet down - using an impact driver.

- Use a 1/4" socket with a phillips head (a longer handle will give more leverage)

- destroy the existing fans (dremel, jimmy bar/wreckers bar, wire cutters through the plastic), then remove the screws and place the new fans in.  (This will only work if the fans sizes are the same)

Good luck!