more on PEX shrinkage (or was it too hot?)

[easternbob]

I had a SERIOUS problem over the weekend with shrinkage (the PEX kind). Got up Sunday morning and heard a weird sound from the basement, turns out it was water going thru the refill valve, not a good sign! Went out to my boiler shed (after shutting off the valve) thinking maybe it over heated the the P&T valve had popped open and was stuck open. Well that wasn't this issue.
What happened was on the hot pipe the compression coupler between the copper pipe and the pex had seperated. To be more specific I think the pex slipped out of the coupler. Sorry didn't think to take any pics until later. There was an inch of so gap between the end of the pex and the bottom of the coupler so plenty of room for water to gush out.
My only other thought is maybe I put a little too much wood in and it went into idle when the storage tank couldn't take any more heat and things got too hot there?? But there wasn't any melted off chunk of pex left in the coupler and the end was pretty clean??

I do know this the pex comes in thru the floor at a slight angle so the coupler to copper might have been stressing that joint since it wasn't nice and straight. So maybe this shrink/swell cycle caused it to come loose?

My plan is to use a full flow ss flexible connector (often found on hot water tanks) to transition between the two. Hope the have the parts by tomorrow...

 

[woodsmaster]

Kind of odd that it took 4 years to come apart.

 

[tom in maine]

Sounds like it overheated. If they system is under pressure, temps can easily go over 180F and cause mischief.
A photo would help, although it sounds like you have sorted it out.
PEX should have room to move.
The rule of thumb is to come off the heating device at least ten feet with copper before changing over to PEX
2 cents worth on a cold night...

 

[easternbob]

No doubt it was warm. But I was looking at the small little piece I cut off to make sure I had a clean end and it looks too clean and uniform to have been melted and then blown out in my opinion. In my mind if a piece of pex were to fail from heat and pressure it would blow out in one spot not a nice even rim all the way round.
I think for what ever reason the pex just slid out of the compression coupler.

 

[tom in maine]

It can just have softened to the point that it slipped (or was pulled) off. The tubing would not have been changed much. If there was some sideways torquing or stress on the joint along with the system pressure, it can happen with overheat. Is also possible the crimped joint was not up to snuff.

I use PEX in our shop for testing boilers and hx. I used copper at my home. Am always there at the shop to keep an eye on things and a mess is easier to clean up in the shop if something lets go.
I realize that PEX is necessary for long runs but it also has a large coefficient of expansion and these things can happen.
My guess is that this problem is more significant with larger diameter tubing. Stresses are greater and wall thickness of plastic tubing is greater.

 

[brant2000]

I've never seen it myself, but can recall watching an episode of This Old House recently in which Richard was demonstrating some interesting characteristics of PEX. He took a blow torch directly to the PEX until it got just about hot enough to melt and then grabbed the end with a pair of channel locks and pulled. The end popped off with a perfectly clean break, just like you cut it with a knife.

 

[700renegade]

My neighbor had three run-away fires in his Buderus boiler with a malfunctioning draft control ( he's a slow learner). Each time it hit 240*+ and split open the 1" pex on a longitudinal axis, not circumferential. about a 3" long 'slit' in the pipe each time.

 

[easternbob]

700,
Thanks for that info.
I guess the mix of things over 4-5 years just loosened up that fitting to the point the pipe slipped out.
Was it the heating/cooling cycle or bad install or funny angle.... or a mix of all of these? I will take a good look at the other compression fittings (I have 3 others just like this one) to see if they look like they are still seated nice and tight. Although not sure what I will be able to see.
What bugs me is I ordered a SS flexible connector from supply house on Sunday and it has not shown up yet. Supplyhouse got it sent right out, UPS is the issue they are taking forever. AND I'm running elec. back up boiler which is killing me

 

[BoilerMan]

Sometimes it's nice to have an economical backup like oil or gas. Electric is convenient, but not as economical as other sources of heat. I'm in the process of finally connecting my Toyotomi oil boiler to heat the house instead of just DHW. With cheap (cough) oil, I want to burn up the old oil and get a fresh fill up of $2/gal oil.

TS