First thing is always to reset the hi-limits (aka protective thermoswitches). Unplug the machine
and remove cover - you'll find two of them at the top of the boiler:
You need to press the little button in the middle, as with a screwdriver in the pic above.
If that fixes it you may still have a malfunctioning pStat or controller relay. That can be hard to chase down if intermittent. Replacing a pStat is easy and inexpensive, so doing that is pretty good advice. Probably is a MaTer XP-110, but be sure you get the right one for the Appartamento- there are different kinds of XP-110.
If the hi-limit reset doesn't fix it it you may have a stuck or burnt open pressurestat, a bad relay or transformer in the controller, a bad/open hi-limit switch, or a burnt open element. Troubleshooting that requires a good multimeter and a little electrical expertise. You can start (with machine safely unplugged) by removing wires to the element and checking the resistance there. (steady reading in 11 ohm neighborhood would be good) and doing the same on the pStat (when machine is cool you expect good continuity (less than 1 ohm) between the two pStat terminals. Both hi-limit switches should also show good conductivity. If the controller relay isn't powering the element, then it gets a little more complicated to troubleshoot.
DaveC wrote:If it blew it's guts through the safety valve (I don't think the vents are routed outside) and water got everywhere, it may have shorted something....usually that would trip any RCD or fuse unless it's gone open circuit.
The pics I've seen of the innards of the Appartamento show a pressure safety valve with a barb fitting and tube, so hopefully all that spray would have been directed to the drip tray. By all means this machine should be kept on an outlet with a working GFCI.