It just failed and PCB failure light TR3 light up. There are four LEDs in total, TR1-4, which I can't find any info about in any manual. Do you have any documentation about lights?
It seems to hold the 1.2 bar boiler pressure even at failure, so heating element is powered. It has 5 bar line pressure (maybe high, we should put in a limiter), which sometimes jumps 1 bar when other appliances use water.
I have to cut the power to reset. It does not have the water conditioner. I've checked the connections, but if it had poor connection, it wouldn't be “fixed” just by resetting? High limit safety, isn't that just a thermostat which cuts only the heating element power (leaving pump and dosing working)? I'll solder two wires to the secondary side of transformer and measure it when it fails (I need to solder, as the PCB is located beneath one group – can't open it and measure while the machine is on). But since TR3 lights, it might be powered, unless this is a direct PCB under-voltage indicator (not running from the microprocessor).
I measured a few caps within the boxed space which contains the PCB. A big circular metallic 5uF 5% cap shows 4.2uF. A smaller 1uF square cap which is in parallell with a big relay reads 80nF. I think both these just smooths external components, not interfering with dosing controls etc.