how can i fix my problems?

hi

i have an vaillant ecotec plus824 boiler and keep giving me an error f75.i have ordered a new spare presure sensor,andthe the boiler engeener my pump is very slow aswel.my question is whether any water is sepouse to be in a ev expantion valve ,i mean.because the system is emtpty and as soon as i atached a pump,water start coming out througt my sensor.i have removed the sensor for the time being