Fascias & soffits are there to protect the roof timbers from the elements - wouldn't be ideal to be blasting them with high presure water - alot of the vents are pretty delicate too.
I find a bit of tfr and my wfp does the trick for domestic fascias, soffits & guttering.
There are however pressure washing lances up to 24' - good for cleaning walls, and roofs - think they have a maximum temperature lower than a steam cleaner - and i'd be carefull not to use a pencil jet
Dave