I had exactly the same problem as in whenever i pushed the lungo button for a normal cup off coffee the water would only pump out for roughly 6 seconds and then stop.I tried the factory reset numerous times and it didn’t make any difference.
What did work was filling the Nespresso water container up with boiling hot water from my kettle.
My theory is that there is something wrong with the Nespresso hot water temperature control and it has become broken or corrupted and therefore effects the volume of water that comes out of the machine.
Anyhow my Nespresso machine now works normally as long as i fill the water container up with hot water from the kettle and has saved me the hassle of buying a new machine.
By the way my Nespresso machine is 5 years old.