I have always doubted vinegar as a bit of an old wives tale but after a few hours, it seems to have done something. I put the portafiler on it and turned on and it strangulated, wheezed, suddenly spat and then started pouring slightly dirty looking water out of (one side of the portafilter at) the bottom.

Either it works now or I may have to try citric acid a few times to clear whatever else is in there? It is being used in an ultra-hard water area and it has never been cleaned since I got it second hand in rural France