There is any solution to fix it, instead of return back to shop?
I also have other problems(bialetti 4tz moka express) - coffee comes out only ~70ml and is very disgusting. No matter if i do it like my italian friend- he pours little warm water-40-60°C, makes a little hill of coffee, and sets fire on little above the lowest gas power. Extraction duration (2min).- one lucky time i get good coffee and a good amount of coffee( ehh i dont know how maybe i need to put perfect weigh of coffee? (2full espresso cups ~2x 70ml) it had a lot of sweet, little bitter and little fine acidity aftertaste.
I try to fill up with 90°C water. Its come more coffee. Maybe(90ml) but always very acidity.