I had a little incident a few months ago where i forgot to put water in my Avanti 10 cup stovetop mokka pot.
It was left on the heat for around half an hour whilst i went up to the shops and asked my wife to take it off when finished brewing. it didnt burble so it didnt get taken off. :-[ had some very heavily roasted coffee in the basket when i got back and it took forever to clean the burnt smell and taste out.
I think due to the sustained heat the pressure relief valve spring has lost its temper and vents everytime i make a brew.
is there anyone that sells replacement valves?