This radiator valve is leaking, I suspect since the plumber drained the radiator as part of a boiler install a couple of weeks ago, the nut is rounded and it's hard to tell if it is (was) square before and I have tried with an adjustable spanner but no joy and don't want to round further - anyone know what size this should have been and any suggestions on how to tighten?
https://photos.app.goo.gl/pVNS1da3yjWHdZYn8
https://photos.app.goo.gl/pVNS1da3yjWHdZYn8