Best way to tighten union?

SteamingatMohawk

The union looks like it is brass, which is softer than an iron based fitting. Be careful to not make things worse, especially creating "low spots".

Jamie Hall

soap won't hurt on the mating surfaces, if you wipe most of it off -- but it's mainly useful as a lubricant on the threads.

mattmia2

Unless it is chunky, something on the mating faces isn't going to hurt anything but it won't help either. I would use a touch of pipe dope on the threads and on the back of the unions where the nut rotates on the back of it but anything that lubricates it will help it from seizing up. Anti-seize or modern types of dope or oil will stay in the threads and make it easier to get apart later.

Dave_61

Wanted to update you guys. Took apart the union. There was a lot of grit in the valve part. Cleaned both sides with 0000 steel wool. Put a little bit of liquid soap on both sides and some blue teflon tape in threads of the union. Had to use a pry bar to slightly lift the radiator while tightening and rocking it. Was not easy to do the final tightening of the nut. Had to use plumbers pliers and offset wrench with a pipe on the end. Snugged it up and no leaks. Also, took a little of the wood floor away from the pipe and wrapped the pipe in a little plastic from a soda bottle where it was still somewhat snug against the wood. Radiator still ticks a bit when first heating, but our other cast iron convectors seem to also do that. Thanks for everyone’s advice!!!

Jamie Hall

BRAV)O! And thanks for the update.

MikeAmann

See, it wasn't as hard as you thought.

hot_rod

If the face and seat is scuffed up badly, then smear some pipe dope on both surfaces

Any lube on the threads, plumbers stem lube, even chap stick will allow the threads to twist smoothly together

nicholas bonham-carter

I think a little liquid dish soap on the mating surfaces and union threads would be better than antiseize,, or pipe dope.—NBC 

billvedovato

A basin wrench will do it. They're made in a couple of different sizes including big enough to tighten that union. I've been using one for all manor of heating repairs through the years. The jaw is thin enough to get into tight spaces and the handle swivels. DON'T BUY A CHEAP ONE!

Kiwi

I suggest going to a engineers shop. Asking for a not of 3/8" or 5/16" or preferably 1/2" scrap steel plate.
Then work out the angle you need and make the spanner your self.
A good spanner doesn't need to be flash looking to be able to do the job.
It may take a bit of time but hey, all you are needing to do it to turn it a very short amount to be able to get a conventional spanner on it for the next stage of the nut's revolution.

The other possible options, MAYBE, is to get to it, from the other side of the nut. Cut a hole in the floor or rear wall, or maybe both. (been there, done that, a couple of times.

I look forward to reading how you managed to 'sorted it'.

Cheers,
Kiwi Will.

george_42

I use a chisle and hammer and drive nuts off or on when access is limited