Heater Matrix Replacement

I have the dreaded no hot air on the drivers side of my car, spoke to local Skoda independent specialist, who said there was a proper kit for flushing out the matrix, for the sum of £1200, and if I just replace the matrix without that, then it might block again.

But being that you can get a matrix for about £100, I could replace it 10 times and it'd still be cheaper, so looking at doing that.

Seems simple enough, I'm not going to flush the system, just remove the matrix from the footwell. Looks like I have a Denso heater, and I've found this, which looks worth a try: https://thecarheatershop.co.uk/shop/skoda-octavia-heater-matrix-2013-onwards-denso-replacement/

I removed the silica bag when I first got the car 4 years ago, garage told me it's probably blocked by casting sand.

If anyone has done the same and has any tips before I get going on it, would be appreciated!