has anyone attached a plumbed line to a PV Lusso? I have seen older Sama and Bezzera clubs with a manually operated plumbed line. In use what does that entail? Can you top-up the boiler when it is hot- and under pressure? I assume if you can you must make only small top-ups to prevent a shock to the element? I also assume you will need some kind of OPV (?) valve?

Any info much appreciated.

If you wanna do manual plumb-in (i.e. no auto-fill logic), all you really need is a fitting on the boiler to hookup a pipe, and then a 2-way solenoid valve on that to stop the flow of water in. You would wire a switch into the solenoid valve, preferably one that is spring-loaded such that it turns off if you aren't actively holding it down to prevent it getting left on. A check valve near the solenoid valve is probably a good idea as well; probably doesn't matter which side it's on.

Remember, if you go for this mod, that if your water pressure is less than boiler pressure (unlikely), filling probably won't work. It's preferable if you have 3+ bars line pressure, I think. If your pressure is too low you will need a pump. A vibe pump would work great, though I imagine setting that up will be a bit more complicated. vibe pumps don't like positive pressure when they're off, so you might need 2 solenoid valves, or something like this:

water incoming --> 2-way solenoid valve --> vibe pump --> check valve --> ample line to isolate pump from heat of boiler --> boiler

You may need a check valve prior to the solenoid valve as well as good measure. I don't know; I've never done this before. I am just telling you what I would try. I think it's pretty safe if you don't kludge it, but keep in mine the risk is all on you! Good luck.