Leak under kitchen sink

[rjbny]

Every now and then we find water underneath the kitchen sink towards the back wall in our E19. Since the first time we noticed my wife has put a rag there to prevent damage. I wondered if the water was due to pressure when turning on the hot tap so we started running the hot water before turning on the heater. Unfortunately, that didn't fix the problem.

Recently we saw a drop coming down the red hot water line below the copper to PEX fitting. I looked around on the web to try and see how that fitting works and whether it would be possible to tighten away the problem but I couldn't find the fitting. Can anyone tell me how the fitting that ETI used works and if the leak can be fixed without replacing it? I'm attaching a photo if the fitting I'm talking about (black plastic fitting in red line).

[Ron in BC]

Your first step could be to try and tighten it a bit. Some caution is required. You can see the flat area on the brass fitting. It's there so that you can put a wrench on it while tightening the black fitting. It prevents twisting the copper tubing.

Also caution is needed on how much you try to tighten it. Certainly don't use pliers etc. Firmly tightened is about as much as you want to go. Breaking the plastic fitting adds another dimension to the situation.

In this type of situation, where the leak is only a drip, I often use a dab of pipe sealant on the threads. Don't use teffie tape as that could allow you to tighten the fitting to the point of breaking it.

Ron

[gmchamplin]

We had the same symptom - occasional water under the sink. I believed that it happened when the water heater was first turned on and before any hot water was used, due to elevated pressure caused by thermal expansion.

Whether or not this was true, my RV shop concluded that it was a cone in the fitting that was compressed and the fitting could not be tightened enough to stop the leak. They replaced both pex-to-sink fittings and we have had no problems since.

[dosby]

After the first winter, I had to replace under sink:
- hot water connector washers
- plastic hot water hose (leaking at one of the ends) with a metal one
- outside shower mixing valve (plastic cracked and leaked to the outside)
My guess is that those parts expand when hot water passes through, then shrink and dry up in the winter, and then fail to expand again next summer

[Escape2Yukon]

We experienced the same situation during our recently completed cross-country journey. So far we've been unable to find the source of the problem. Thanks for the comments and suggestions so far; we'll see if we can check some of these things further (with limited time before we must winterize the trailer!).