I woke up 12:00 on Sunday night to the sound of my smoke detectors going off and the sound of water and steam gushing. Went and opened my basement door and was overwhelmed with steam and couldn't see a darn thing. I grabbed a flashlight and headed down to the boiler the temp gauge was maxed out and pressure was at 0. I shut the primary and secondary air to slow down the burn. I found the pex that ran above my flue pipe had exploded and that's where the steam and water was leaking from. I isolated that zone and then confirmed that there was still some water in the boiler. I manually opened the relief valve and pulled out a pipe plug just to be safe. The boiler was still making steam because there was no pressure. I started to fill it back up real slow because I didn't want to temp shock the steel. Meanwhile my wife is running around vacuming and mopping up the boiler water that had gone into several basement rooms. After about 1/2 hr the boiler was full again cooled off and holding pressure. I Checked the fire and it was still going but now just a bed of coals. We finished cleaning up for the night and let the boiler run in oil mode. So I guess you never want PEX above the flu pipe even if it was 20" above it's still not enough under certain conditions.
Pex blew up
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Nofossil
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Sounds like a real mess - glad no one was hurt. That PEX looks like it's burned - is that what happened? I'm curious about how and why it failed, and what precautions might be indicated. I would have assumed that 20" was plenty of clearance above a flue pipe unless something really unusual is going on. What was your pressure relief set at?
Thanks for sharing your disaster.
Thanks for sharing your disaster.
Redox
Minister of Fire
That does look a little charred. Is it possible that it drooped down when it got hot?
Keep in mind that PEX is still plastic and its burst pressure goes down quickly with temperature. If it was carrying 180F water and the ceiling was 120 and the radiant heat from the stack was warming it up, you might have had the perfect storm. Obviously time for a little redesign... :smirk:
Good to hear your boiler survived the incident. It could have been much worse!
Chris
Keep in mind that PEX is still plastic and its burst pressure goes down quickly with temperature. If it was carrying 180F water and the ceiling was 120 and the radiant heat from the stack was warming it up, you might have had the perfect storm. Obviously time for a little redesign... :smirk:
Good to hear your boiler survived the incident. It could have been much worse!
Chris
Dave T
New Member
DAM you should have put a disclaimer on your thread title VERY GRAPHIC may upset the stomach of boiler owners, you were lucky to be home when this went down (although I am sure you felt anything but lucky)..Sorry for my rudeness Welcome to the boiler room very dramatic second thread, In my opinion 180 degree pressurized water going through that pex is boarderline to begin with must be the small amount of heat that the chimney produced was enough to burst that line..We all feel for you and hate to hear another fellow boiler operator had to experience those conditions I am glad you posted you may save somebody from running their pex anywhere near the chimney I would think 20" would be ok but I guess not..Good luck with the repair..Dave
free75degrees
New Member
Do you think it is possible that the pex had a deep scratch in it? Funky mechanical things can happen to objects when they get scratches and nicks in them and then are subjected to large forces.
heaterman
Minister of Fire
Look's like it burned through from the outside in. I would guess that a combination of high water temp and proximity to the flue pipe caused that failure. Pex will become very pliable at higher temps and I often see it installed with inadequate support. I would guess that possibly you had an over temp or a no flow situation which caused the pex to sag onto or very near the flue pipe. The surface temp of that was probably what caused the rupture. Almost any size pex should be supported every 2-3' at 180*+ temps otherwise it turns into spaghetti.
Dave T
New Member
I think REDOX nailed it when he said it drooped when it got hot and the end result was a lot closer than 20"..
Was the pex free floating over the chimney? If so get ready Mr George Clooney here comes the storm..Dave
Was the pex free floating over the chimney? If so get ready Mr George Clooney here comes the storm..Dave
stee6043
Minister of Fire
I tend to agree with the above posts. It sure looks like it made contact with your flue. The black charring wouldn't have been cause by hot water alone...
This has bolstered my respect for heat generated above hot items even more! Years ago we had a set of glass shelves with an array of 5 shelves spaced about 18" apart. The wife lit a single small candle (one of those tiny ~1" diameter x 1.5" tall jobs) on one of the shelves. About 20 minutes later *CRASH* the shelf above the candle shattered. We just looked at each other in amazement...then put the fire out. I never would have thought a single small candle could put out enough heat to crack glass 16" above the flame.
Glad to hear there was no irreparable damage. But definitely sounds like time to re-evaluate the set-up and look at all the materials which are above the flue pipe. PEX, wood joists/rafters, etc.
Glad to hear there was no irreparable damage. But definitely sounds like time to re-evaluate the set-up and look at all the materials which are above the flue pipe. PEX, wood joists/rafters, etc.
I'll be installing next week or two. You just talked me into copper. Expensive, slow, but solid. Everytime I read about pex, I see all sorts of stuff regarding expansion, followed by susceptibility to scratching off the 02 barrier. Don't all these supports with all that movement result in scratching?
BrownianHeatingTech
Minister of Fire
penfrydd said:
Slow in terms of water flow, too - all those fittings mean you have more head loss with copper than pex. Don't forget to account for that in your pump sizing.
penfrydd said:
Not if done correctly. Pex should not contact things like metal which can scratch it.
Joe
I've been reading every post in the boiler room for all most a month and Okay, so what is best? I am having my Tarm 30 installed within a couple weeks by the plumber whom I purchased it from. My oil boiler is 35 feet away from where my Tarm is located. Currently have 2 baseboard zones but want to add a sidearm for my dhw and planning on a Modine in the basement for overflow and or heat down there if I want it. Thanks in advance.
The pex was 3/4" Wirsbo HE pex, it may look a little funny because there was black foam insulation on it which melted to it. The pipe was not touching the flue and was still at regular height when I got to it. I may be possible that it droped when hot and then raised back up when the leak started. It could have had a scratch in it but i'll never know now. Anyway I will only use copper in a location like that from now on and then switch back to pex after the heat danger. I think I'm going to add extra heat sheilds over the flue also just in case.
I forgot to mention, I have never seen so much steam in a house at one time. It was amazing like a free sauna 
Redox
Minister of Fire
heaterman
Minister of Fire
BenW said:
If that is indeed the case, it would seem that you had a severe over temp situation for some reason. HE pex is rated 80psi@200* so I would surmise that your temp was somewhat higher than that. Once any pex gets above 220* or so the pressure it will sustain diminishes rapidly. Is it possible that your system stagnated (No flow) for even a few minutes?
Ben, sorry to hear about your pex, I had the same thing happen friday night. I had let the fire burn out(few coals remaining) and shut my circulator off to work on swapping my supply and return lines on my burner. Got distracted from the job at hand and it turns out a few hot coals in the bottom of the stove was enough to make steam. Found out by wondering why my pump was running and wouldn't shut off. Opened the cellar door to hear water gushing into the basement from the burial tube. Again, I feel lucky to have learned the lesson with no one getting hurt and no damage to the boiler. I only have to replace the pex (70 feet) which thankfully is pulling fairly easily. It burst 3 feet under my garage and I pulled about 12 feet out to see if I could trim it back, but it is so distorted that I'm going to be on the safe side and replace the whole thing along with my apparently defective t&p;valve. This also leads me to an interesting question. Does anyone have any type of battery backup (computer UPS?) to run their circulator pump when the power goes out?? My grundfos runs .75 amps on high speed and .55 amps on low and am checking into what kind of time I can get out of one of the backup supplies to ensure that I won't be replacing underground pex again. I am interested in hearing what anyone else is doing for peace of mind when utilities fail, but the fire burns on.....
hd45hunt said:
Start a new thread and ask 2.beans how he did his. He used an inverter with a battery back up. I believe that his circulator can run for nine hours after the power goes out.
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