Quick response asap please - Relief valve leak All aspects of plumbing questions and answers, help, tips and information

[StongBrew]

Hi. Need a quick bit of help, nothing like a bit of Friday night plumbing.
Noticed boiler had lost pressure so gone to top it up and noticed a leak from above pic, guessing its a pressure relief valve? The black cap on top is slightly loose, done it up and it does stop the leak but should this be done up tight or is that a stupid question.

Regards

[StongBrew]

Attached pics now of leak:

[proptech]

Hi StrongBrew

That is an automatic air vent. Tightening will stop the leak, but, you will have to replace it. In normal use the cap is left loose to allow the air to escape, water is contained by a float valve.