a while ago I purchased a second hand Mininova EVD (vibe/volumetric). The Mininovas have both the hot water and the brew water running through their own heat exchangers.

I'm still trying to work out if this is a good design feature or not. The only way water can normally escape from the boiler would be via the steam valve, which would naturally leave every bit of sediment, scale etc inside the boiler, probably making it scale faster. It would also make the descaling process different to other machines.

Just curious as to other's thoughts, particularly those who have worked on double HX machines.