How to use Loctite 290 to fix a pin hole leak

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#1: Post by beer&mathematics »


I have a very tiny pinhole leak at the joint from a pipe leaving the boiler going to the steam wand, the green arrow points to it in the picture below:

For extra context, you can check out my (glacial) progress on fixing my Bezzer Family Lever here.

You can ignore all the red arrows since I fixed those leaks by simply adding plumber's tape.

However, the green arrow is a pinhole leak at the solder joint. After searching HB extensively how to fix this, I see that using Loctite 290 seems to be appropriate here.

However, I haven't seen any detailed instructions about how to actually use this. Can anyone add clarify what I should do?

I already emptied the boiler last week (about 5 days ago) so it should be pretty dry and also bought the Loctite 290.

Thanks in advance!
LMWDP #431


#2: Post by Al_Mahka »

Hey b&m

I can't tell you how to fix the pinhole leak with Loctite, as I've never done that before and I likely wouldn't attempt it.

The best way to fix it is to get a torch, flux and solder, pull apart the joint, clean it up, and re-solder. Lots of vids on youtube that show how to do this if you have never done it before.

Good luck!


#3: Post by nahau »

If you want to fix it correctly, you should solder/braze the connection again. If you can't do it yourself, you could try a radiator shop and ask how much it would cost for this small a job. If you insist on using Loctite, the TDS should have all the information you need. ... lant=WERCS

Freddy Camacho

#4: Post by Freddy Camacho »

Since you have bough the 290. Might as well give it a try.

I have successfuly fixed few mini pinhole leaks in my cremina using 290. It works wonders.

Get the boiler or in your case pipe super dry...the a few drops over the pinhole leak...and let it cure 1/2 day to a day.

For a slightly larger pinhole leaks...i did experiment 290 with cotton gauze (? The one they used for multi stage water filtering system). Just chop em up and sprinkle a little over the pinhole and 290 it.

Works fine.

Cant comment on the food safety issue. But it was purely an experiment. Since i have plenty of 290 left that is expiring soon.

Been following your thread...good luck... you are almost there


#5: Post by Nate42 »

loctite 290 is very thin, it is designed to wick between threads after they are already mated. It needs absence of air to cure. If you have a very small pinhole, it will wick into the hole and cure. If the hole is too large it either won't cure or won't seal the entire area because it is so runny. I personally have had mixed success using it as a boiler sealant. Had better luck temporarily using hard water and let the pinhole "heal" with scale.

Its not technically food grade, but its non toxic and there is such a small amount that I can't imagine any health or taste impact.

Its worth a shot, may as well try it. Good luck!

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#6: Post by beer&mathematics »

Thanks Freddy and Nathan for the encouragement! :wink:

Last night I went ahead and descaled the boiler with citric acid (30 min, the 3 clean water rinses). Looks clean in there and I left it to dry overnight.

This morning I borrowed my SO's hair drier and dried the area for a few minutes to give it extra dry time.

I realized when bringing the boiler up to pressure a bit while descaling last night the the green arrow has no pinhole leak in the first photo of this thread--that area is perfectly fine.

The actual pinholes are with the solder of the pipe to the boiler, as in the picture below:

The pinholes are so tiny that you can't see them with the naked eye, only after you bring the machine up to pressure do you see tiny bubbles gently surface.

Based on this, I am going to give the Loctite 290 a try and see if it holds. If not, then I'll take it to a radiator shop as suggested to have them braze it.

Thanks again HB for helping me with this project!
LMWDP #431


#7: Post by XS750AU »

Most loctite products degrade when subjected to heat, what is the temperature rating for 290? 290 may be a viable short term patch.
The most durable solution to your problem is to have it resoldered. The loctite will contaminate the joint and make a solder repair more difficult in the future.


#8: Post by Jeff »

Loctite 290 TDS

While it does discuss how to use the product for "porosity sealing", XS750Au's point about contaminating the metal is a good one. Though it's possible that the heat and flux of brazing would remove the Loctite if/when the patch failed or new leaks appeared in the same area, re-brazing that connection is the path I'd take.

The NSF-related information on the TDS isn't terribly reassuring (highlights mine):
NSF International

Registered to NSF Category P1 for use as a sealant where
there is no possibilty of food contact in and around food
processing areas. Note: This is a regional approval. Please
contact your local Technical Service Center for more
information and clarification.

NSF International

Certified to ANSI/NSF Standard 61 for use in commercial and
residential potable water systems not exceeding 82° C. Note:
This is a regional approval. Please contact your local Technical
Service Center for more information and clarification.

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#9: Post by beer&mathematics »

I went ahead a applied a tiny amount of Loctite 290 around the leak. I'll let it cure for a few days (I'm not in a rush).

I'll report back how it goes.
LMWDP #431

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#10: Post by bluesman »

Effective treatment requires an accurate diagnosis. A wicking sealant will not "fix" problems like a tiny, early fatigue crack or damaged threads. Further, the material to be sealed has to be spotless for the compound to work - and the deposits that tipped you off to a leak coat the walls you're trying to seal. So using 290 to close a leak of uncertain origin is a leap of faith. Hope and luck are poor interventions.

You have to take a leaking assembly apart, clean it thoroughly, and inspect the pieces carefully to find the problem. If a soldered or brazed joint is leaking, it has to be redone. Even then, a few issues will not be obvious. But this approach has the highest likelihood of success.