At a glance Tony,
It looks to be the Anti-Vacuum Valve. These will spit and bubble a little as the Boiler heats up but once the steam production is sufficient, the valve should seat under pressure and all further sounds or observations of apparent leakage should stop.
If yours is leaking continuously with the Boiler up to normal temperature and pressure, then the valve will need to be either replaced or reconditioned. Since they are quite cheap to buy, youre probably better off just buying a replacement this time around and then recondition the old one so youre ready for the next time...

CoffeeParts have them here... part #618968 http://www.coffeeparts.com/sanmarino...e-parts-7.html . Would also be worth your while to grab a replacement washer/gasket too, part #524554.
I dont know what the part circled in Blue is.... It could be an OPV but that is just a guess... :-?
All the best,
Mal.


. Can someone also teach me how to change that? Any precaution?
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