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Old 06-13-2008, 09:50 PM   #1
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Union Thread Sealing


I recently installed an Indirect Water Heater and it came with union fittings on all inlets and outlets. I have had problems getting two of the fitting to seal. I did not use dope or tape as I thought it was not necassary on these fittings. Does anyone know what the best practice is for sealing these unions? Should I simply load it up with dope and/or tape?

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Old 06-13-2008, 10:41 PM   #2
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Union Thread Sealing


Where the union connects into the pipes, you need to use a few wraps of teflon thread tape. I'm assuming they're conventional unions with tapered "NPT" threads. The threads in the union's internal coupling (where the union comes apart) do not require thread tape or sealant. Actually, tape or sealant will prevent the union from sealing.

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Old 06-13-2008, 11:59 PM   #3
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Union Thread Sealing


If your mating surfaces don't match up really really really really really really close, almost perfectly, you probably will have problems.

We've only used dope in instances where we're resealing an old union.

Are the unions soldered onto the water heater, or are they thread on type unions?

If they thread onto a nipple on the water heater, you do need to wrap tape on THAT joint.
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Old 06-14-2008, 09:45 AM   #4
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Union Thread Sealing


Union faces and the nut threads should not need any sealant or pipe compound. These are machined surfaces. Sounds more like a bad fit-up between the piping and one of the union halves.
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Old 06-14-2008, 09:45 AM   #5
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Union Thread Sealing


The union is a straight thread Joint and the fittings are soldered into the Water Heater. So, if the mating surfaces are not really close (and I'm gonna assume they were not since they leak), is there another option other than unsoldering the fitting and installing a new one?
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Old 06-14-2008, 12:16 PM   #6
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Union Thread Sealing


Quote:
Originally Posted by dave2008 View Post
The union is a straight thread Joint and the fittings are soldered into the Water Heater. So, if the mating surfaces are not really close (and I'm gonna assume they were not since they leak), is there another option other than unsoldering the fitting and installing a new one?
If you unscrew the unions, the halves should line up almost perfectly, and almost be touching. They shouldn't pull away from the other half and be at some odd angle...

You shouldn't need a new union if this is the case, you might need to extend or shorten your water lines.

can you post a picture of the heater/unions/waterlines connecting ?

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