Radiator valve leak; how to repair?

hadeone

I noticed one of my radiators hissing by the valve and discovered the valve leaking from the nut connecting to the radiator:

What is the best way to resolve this?  Undo the nut, add dope and retighten?  

Thank you. 

Jamie Hall

The "nut" connecting to the radiator is almost always the clamp nut on a union. The onlyy way,, really, to handle a leak is to undo the union completely (if this is hot water, you have a problem... water water everywhere) and clean the mating faces of the union. They must be clean and smooth -- no scratches. But use no abrasives on them. Then make sure everything lines up properly -- you can't use the nut to pull things together. Some people like a VERY thin smear of dope on the mating faces. Some swear by a little dish soap. Some don't use anything at all. Then put the union together. Then tighten the clamping nut hand tight -- it isn't sealing anything, so no dope or anything is either needed or useful -- and then tighten in another half turn with a wrench, but no more than that. If that does't fix the leak, undo the union and ccheck again that it is clean and smooth and that everything is lined up.

hadeone

Thanks for the thorough explanation.  I should have been half as thorough in my description but I forgot to mention it’s a steam system.  

It does look like a clamp nut. I’ll support the radiator and follow your instructions. Thanks again.