OSM does not fully support post code search, but I find that on device routing is a very poor option due the garmins inbuilt algorithm that can send you on some very long and seemingly uneccessary detours.
My Garmin used to be great at navigating, but it appears the routing algorithm changed at some point, and sometimes 15 mile journeys would become 60 miles if I followed the Garmin.
OSM does not fully support post code search, but I find that on device routing is a very poor option due the garmins inbuilt algorithm that can send you on some very long and seemingly uneccessary detours.