yes it is kind of the same as with washing machines. Leave the lines pressurised at your own risk. Sooner or later, and it could be 20 years later. Or it could be in the first week of delivery of a brand new machine with a dodgy inlet water line. Its a gamble I am not willing to take as I have seen the results first hand several times. OK in terms of leaving your machine "electrically" switched on indefinitely (& ignoring the above & the need in tnat case, to leave the water line pressurised).... All components have a "designed in" service life. If you leave something switched on indefinitely, even if you only actually use it for 5 minutes per day, its still ON 24 hours per day. Under that scenario, the first to wear out (literally) on your semi commercial will be the pressurestat/microswitch. Rubber seals will harden prematurely through being affected by heat, so the group seal will probably start to allow leaking over the top if the group handle a lot quicker than on a machine that is only switched on and off when being used. The same goes for the steam and hot water tap seals. Etc. Essentially then, you "wear out" your machine faster for no gain in use, especially considering that semi commercials are ready to brew coffee within say 12 minutes, and that accounts for the group thermosyphoning to a proper brew temperature, not just for the boiler to go to set pressure (which it will do in about 6 minutes) Hope this helps give a more technical or academic slant on the subject. Regardz, FC.
