Look at the air break assembly (usually behind left side panel). The water filling will sound hissy but will appear to be OK. The venturi in the air-break gets scaled up and drastically reduces filling speed. This in turn causes the machine to “retry” filling and eventually E1 fault – not filling to capacity in the allotted time. I’ve tried descaling these units without much success – new part (surprisingly expensive for a plastic box!) is the only surefire answer.