3 of 8 Radiators Leaking at Union Nut in a 1-pipe system

SpencerB · April 7

Hi all,

I got such great help here last time that I thought I'd try to lean on the collective experience here again. One-pipe system with a 3-4 year old Burnham/US Boiler rated for 130 MBH or 534 sqft of steam. I calculated an EDR of 311 for my previous post (https://forum.heatinghelp.com/discussion/200276/balance-issues-in-a-single-pipe-system) where everyone helped me fix my venting situation. The issue I'm looking to deal with now is that 3 of the rads leak at or near the union nut. Two upstairs and one downstairs. This only happens when it's below 40 overnight and the steam is running for a long time during the 6am warm-up. In general, my system knocks but not in a dramatic way. So I'm not sure if we're talking about wet steam or just loosened fittings. Either way, we do expect to move out in the next year, so if I can avoid a thousand-dollar repair bill, that'd be great. Having to empty little deli containers every other day or so is a small price to pay to not ruin the floor/ceiling, but it is an inconvenience…

Here is a video (https://drive.google.com/file/d/1GQdOTfGXTCuxKatLXe1zVFPgeVYk9ofn/edit ) showing the most dramatic scenario. In addition to the nut, you can see water coming off the main rad — this is rare and only happens when we leave for a week and turn the temp down to 55-60, so this is not typical. It may just be running under the rad and dripping from that point.

Any questions or ideas are greatly appreciated!

Jamie Hall · April 7

It will either be very simple — or a bear. So might as well try the very simple… what is needed is to recognize that unions are wonderful, but will not tolerate any misalignment, either laterally or vertically — or angularly. The two pipe must be exactly in line. Also, the two faces must be really clean. So — take the union apart (with the heat off!) . Support the feed pipe wo it can't move! Thencheck the faces for foreign material or scratches. Clean them thoroughly. Then do whatever shimming or moving is needed to bring the spud from the radiator exactly in line with the other half of the union. Be fussy. Then I like to take just a bit of dish soap and smear a very thin layer of it on one of the faces. Some folks don't use anything. Then pull the union nut up. Strong hand tight plus no more than half a turn with a wrench should be ample for steam pressures.

You are not using the union nut to pull things together — just to hold them there.

Try that. If that doesn't work, come back…

pecmsg · April 7

A Little never seize on the back of the nut and threads goes a long way.

Steamhead · April 7

I'd simply try tightening the union nuts first. And if that doesn't work, try @Jamie Hall 's suggestion. Worst case is you'll need to replace the valve, including the spud that threads into the radiator.

Larry Weingarten · April 7

Hi, For what it's worth, I like to put just one turn (or a bit more) of the thin teflon tape on the union threads. This lubricates and lets you snug things up a bit more.

Yours, Larry

Jamie Hall · April 7

https://forum.heatinghelp.com/discussion/comment/1893831#Comment_1893831

Um. Try. But be careful to not overtighten the union nuts. They crack very easily — and then you are in trouble! If you are into feeligg torque, 5 to 10 pound-feet is more than enough.

EBEBRATT-Ed · April 7

Unions are funny animals.

I have had 1 1/4, 1 1/2 and 2" unions frozen together that a 2' wrench with a cheater doesn't work. A couple of raps with a hammer will usually get them to break loose very easily.

Same thing works when tightening a leaker. Use some never seize.

If it leaks have someone give it a few taps. You would be surprised the union you think is tight can be tightened more.

SpencerB · April 8

Thanks, all. I'll be brave and try to tighten, then report back. Not quite so brave as to disassemble yet — maybe once it gets warmer up here in NY!

Intplm. · April 8

Pipe dope on the face/ground joint of the union when properly aligned works wonders. Give it a try.

STEAM DOCTOR · April 10

There is really no need for shut off valves, on one pipe systems, unless you are talking about an apartment building or something like that. And your standard residential home, they are pointless. And they are probably the biggest leakers in the system. There is almost never a good reason to shut off the valve. So then what's the point? If this was mine, and I was replacing the valve, I would use an elbow and a union instead. With a few nipples. If you really want the ability to shut off the radiator, then use a 1/8 inch ball valve on the radiator vent. Dhal makes such a valve

Steamhead · April 10

You mean "Dahl"?

STEAM DOCTOR · April 10

Yes. Old finger typo

STEAM DOCTOR · April 10

Dahl makes really high quality valves. Been very happy with their products

ethicalpaul · April 10

Hopefully any brass 1/8 npt ball valve can stop 2 psi of air pressure. Maybe I'm just an optimist!

SpencerB · April 13

Thanks for the suggestions, all. Putting in an extra 1/2 turn worked wonders on the biggest leaker, but the other two won't budge under my pipe wrench. I'm fearful of cracking the nut, but maybe a cheater bar or a couple quick hammer raps make sense? I wonder if I should just source a couple replacement nuts in case things go awry. One of the rads in question has all its hardware painted, which is so much more annoying. the point about the uselessness of the valve is well taken, especially in these rooms so who knows maybe there's an elbow in my future. Anyway, will add more on what happens next!

ethicalpaul · April 13

No, don't use a cheater bar or beat on the nuts. This is not fixed with more force.

You can disconnect the union, slide the radiator away and clean the facing surfaces of the union with a gentle scotchbrite pad, then make sure the radiator is aligned and re-unionize it.

Gently rock the radiator as you tighten the union nut in order to help convince it to be properly aligned.

You can't replace the nut—you basically have to destroy the spud (which captures the nut) in order to remove the spud from the radiator, and doing that means you have to replace the valve (or go valveless with other fittings) anyway.

3 of 8 Radiators Leaking at Union Nut in a 1-pipe system

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