Why not use a cleaning solution, instead of a pressure washer??
I used to use my power washer to clean my patio, but have found a great product called Dairy Hypochlorite. You simply dilute it, pour it on (I use a watering can), agitate it in, leave it a few minutes to do its stuff, then swill off with water.
This is the stuff I use:
https://www.evansvanodine.co.uk/shop/product/173-r064kev-r064nev-r064sev/
£11.55 for a 25 litre tub, although there will be postage to add on top:
https://www.quillproductions.co.uk/products/dairy-hypochlorite-25ltr