fix the connector leak to water pump - emersion heater

[Kiko]

hi all,
i need help to fix the leak from a pipe connected to the water pump via flexi pipe and it is feed from the immersion heater.
I have emptied the water tank in the loft and also closed the main stopcock. still the leak is on - hoping it will eventually stop.

I have not idea how the water tank in loft and emersion heater and the water pump all work together..
but need help on how to fix the small leak as well.

in the attached file the area marked is leaking under that bolt
any help is appreciated pls