It’s a ■■■■■■ pump/nozzle. You have to get the nozzle angle right, keep wiggling it slightly until you get a steady flow - holding the trigger gently at first then depressing it fully once you get the steady flow. It will probably switch off again after 1l but once you’ve found a good nozzle angle keep it and re-press the trigger. It’s annoying but our services have been like that forever.