leaking dielectric union

Ross_7

I usually use Brass NPT x Sweat Union. I've never liked di-electric unions.
Ross

Dave_118

leaking dielectric union

We have several dielectric unions in our hot water/glycol heating system. They are soldered to 2" copper pipe on the side that has the gasket/large nut and threaded on the other.Over the past 18 months since it was installed, I have been able to tighten one or another when they start to drip a little.
However, there is one near the boiler outflow that I cannot cinch up. The thing is as tight as I can get it but drips intermittently. I haven't been able to find where the leak actually is. Whenever I check it, the connection where the large nut/rubber gasket is is dry, but there will be a small amount of liquid in the coffee can I placed under it. If I had to bet, it is leaking not at the nut, but between the copper pipe and the gasket.
Where do these typically leak and are there any tricks to get it to stop? Is the gasket replaceable without having to cut/resolder the copper connection?
Thanks.
Dave

hot_rod

If it is zinc or galvanized plated

it shouldn't be in a glycoled system. That plating will react with the glycol.

Any way to use a copper to female adapter and possibly a 2" copper repair coupling to get it all together?

I'm not a fan of dielectric unions in heating systems. There is no reason to use them. Corrosion will not occur or electroylsis in a closed loop system. Especially one with hydronic glycol. Hydronic glycols have inhibitor packages that will scavanage any small amounts of O2, and also buffer the ph.

Are diaelectric unions even rated for that operating temperature?

hot rod

Unknown

I seconded

I seconded what Hot Rod said and also not a big fan of these unoins at connection of gas water heaters... pipe them straight into gas water heater with copper male adt, never had problem with it compared to bs glav nipple and dielectric union as codes required here in Illinois..

Dave_118

Would that mean

that I would have to remove the soldered connection? Or just replace the threaded half?
By the way, the threaded part does not look galvanized but more of a painted gray color of iron I guess.

RJ_4

Valve off the line, open up the union and check the rubber face washer, it might have got pinched during installation. I agree, using a sweat by mpt (male union) is the better way to go.

Mars_3

WH unions

I ve had good luck coming out of the W/H with a threded brass nipple and going into a FIP brass union, then out to the system in a copper MIP. Seemes to me I heard from ME at one point in time that the Brass acted as a dielectric divice.

Mars_3

WH unions

I ve had good luck coming out of the W/H with a threded brass nipple and going into a FIP brass union, then out to the system in a copper MIP. Seemes to me I heard from ME at one point in time that the Brass acted as a dielectric divice.

Mars_3

WH unions

I ve had good luck coming out of the W/H with a threded brass nipple and going into a FIP brass union, then out to the system in a copper MIP. Seemes to me I heard from ME at one point in time that the Brass acted as a dielectric divice.

Dave_4

experiance is a hard teacher...

The plastic insert in dielectric unions crack from expansion and contraction and then the unions walk apart slowly,
You can replace them with similar metal flanges on each side – and use fiber washers on the nuts and bolts, and wrap electric tape around the 1/2-3/4 inch that goes through the flanges

OR

Forget about this dielectric nonsense altogether, didn’t seem to bother the dead men much!!! What, the laws of physics are different now?