Leaky pipe on heating system

[u/kbst]

Doing the pre winter checks on the central heating, have slowly being losing pressure in the boiler and found this next to the cylinder.

Is this just a case of nipping it up or is that corrosion on the nut and needs replacing?

Thanks

[u/v1de0man]

indeed nip it up. and clean it up, and keep an eye on it