Help Needed Danfos Box is Leaking After Replacing Expansion Tank

[carl160877]

Hi

I am a novice and I do not want to complicate things. Attached is a picture of a white box called danfoss that is leaking in the hot water tank cupboard. I have recentky replaced the expansion tank and the pressure relief valve so I can do a bit.
If you see the two pictures, its the white box on the far right. When I push the switch it seems to kick start the heater tank.

My issue is that when the heating is off I get a slow weapy drip from the bottom of the white box.

I have found the part on line. But as with all things, nought is usually straight forward so I wonder if its the white box or the connection pipe to its rear.

Can anyone help????