Onix Tube

DH123

I have a small radiant system comprised of (3) 3/8" 160' loops. I helped a plumber install the system in
2000. Worked great until about a year ago when the system wouldn't circulate. I can't positively determine
if I have a leak or is taking on air because of the pipe design. This past summer I did extensive testing and found I did have air leaks at the manifold where the onix pipe made connection at the ball valve. I replaced the complete manifold. I can run water through the pipe with no problem and I see absolutely no evidence of a leak. It seems as though I can purge the system and I get air back in the system quicker than before?
Any suggestion...

hot_rod

Check the circulation pump. If water from a hose connection flows through all the loops, when you fill and purge,then the pump must not be working, or you have an air lock.

All the valves in the open position?

kcopp

As HR said check the circ pump. What is in there now?
Another possibility is that the system may have developed sludge in the system to the extent that the circ cant overcome the flow restriction.
I have seen plenty of systems that have Onix tubing in them and are fouled after a few years of operation Most of those systems are Dry/ Staple up systems that run at higher water temps. (worked on 2 this week)
I would add a system cleaner and swap out for a 3 spd circ.

Derheatmeister

Let me guess, Plate-less staple up...
Remember the advertising: Look ma, No plates!
We have seen many problems with Onix....The Manufacture claims that they have a Oxygen barrier.We just removed 500 lbs of this tubing three weeks ago.. If removal is not an option we will reverse flush these systems, Install a system cleaner like the F5 from fernox and use only none ferrous materials. System fluid maintenance is very important ! Especially for this kind of tubing. Sacrificial anodes get eaten alive by this tubing !
BTW: Watts radiant does not even offer this tubing in Europe...I wonder why?

DH123

I haven't got any sludge, When I purge the system after the first bucket it looks as clean as drinking water. The cir is a Taco 1/25 HP. I'll switch it with another zone.

hot_rod

If the fluid ran clean when you first opened and drained it you may be fine.

As Richard mentioned it takes a fairly good flow from a high volume/ pressure pump to dislodge sludge. The sludge is basically corroded ferrous components in the system, it is heavy and tends to lay in the lower sections of the zones and loops.

If you get it up and running and it covers the load on the coldest day, let the sleeping dog lie.

DH123

I switched the cir with another and purged the system again,
(getting pretty good at that). Doesn't appear to be the cir it's working fine on the other zone.

Does anyone know how long mixing valves are supposed to last, this one is 16 years old and it's either not getting a good flow or it's worn out, I can't get over 110 degree F.

One last thing if my excess oxygen is proven to be coming from the Onix pipe which is buried in the slab would anyone consider a heat ex changer with an isolated loop and would this eliminate the oxygen problem?

Solid_Fuel_Man

I would install a HX, and make it a separate closed system. That way you can treat that part of the system and monitor. No need of it letting oxygen into the rest of your system.

Taylor

hot_rod

DH123 said:

I switched the cir with another and purged the system again,
(getting pretty good at that). Doesn't appear to be the cir it's working fine on the other zone.

Does anyone know how long mixing valves are supposed to last, this one is 16 years old and it's either not getting a good flow or it's worn out, I can't get over 110 degree F.

One last thing if my excess oxygen is proven to be coming from the Onix pipe which is buried in the slab would anyone consider a heat ex changer with an isolated loop and would this eliminate the oxygen problem?

Certainly any mechanical device can fail, more often the cartridge is stuck inside the mix valves. Either disassemble and clean, or replace it.

Sometimes with a valve that old the o-rings have worn. Replace the cartridge, or entire valve for a few more $$

Oddly not all Onix systems sludge, I don't have an answer for why some constantly sludge and others never do. Higher operating temperatures certainly coax more O2 into systems.

If you don't , or haven't had a sludge problem, no need to isolate the system with a HX.

I do like hydronic conditioners like Rhomar as an extra protection. They contain O2 scavengers as one ingredient. They do need to be used with quality low TDS water to maintain the inhibitor package.

kcopp

Here is some of the fluid I collected from that system. There was about 2 1/2 gallons that I let sit over a couple days. This sludge settled out of suspension. I grabbed a magnet and sure enough it picked up the sludge great. So this is most likely the inside of the CI boiler.
That being the case a low mass copper or SS boiler would have less of an effect on the water quality.
HR...the latest Coffee w/ Caleffi was really interesting on the nuts and bolts of water quality.
This system would be a good candidate for a power flush.

hot_rod

IF you have considerable O2 ingress every single wetted component would need to be non ferrous to stop the sludge formation that you identified.

A non ferrous boiler would help solve some of the issues, but any cast iron, steel, black nipples will still suffer from corrosion.

Really all metals can suffer corrosion, if the conditions are present to allow it. We have seen brass dezinicifaction, aluminum degrade, attacks at welds in stainless construction all related to the fluid and the conditions it lives under.

There is not an easy, inexpensive fix for those high O2 ingress system. isolating the tubing, if that is the source of O2 ingress helps. An O2 scavenger chemical regiment is another, but ongoing.

The sooner you catch the problem the better, as Richard has experiences, some tubes plug beyond salvageability. Then you look at another heat distribution option.

It can be kept under control with proper, ongoing care and medication.
It does put the homeowner in a precarious situation. And after nearly 20 years since the non barrier tube was introduced, and installed it still haunts our industry.

DH123

I'm replacing the mixing valve tomorrow. Thank you for the pictures Kcopp I can pump a 5 gal bucket full and it looks like drinking water. I've earned a lot messing with this system, thank you to everyone that has responded. I'll keep you posted...

DH123

hot rod,
BTW
Just watch your video from Caleffi.
Installing a 521 w/temp gauge in the AM.

Mark Eatherton

Onix has an oxygen barrier (mylar) built into the tubing. Oxygen can NOT ingress straight through the walls of the tubing.

With that said, everywhere that there is a barbed fitting (manifold connections), between the barbed fitting and the mylar, there is a path for oxygen to ingress, albeit a small path. But if you have a BUNCH of connection to the manifold, these small paths can and will add up and allow significant O2 ingressions to occur. Rust never sleeps...

Historically, there have been three proven methods of problem avoidance.

One is to use all non-ferrous components.

Second is to use a non ferrous heat exchanger to isolate ferrous components from non ferrous, and keep all components on the load side (pumps etc) non ferrous.

The third, and least reliable way is to maintain corrosion inhibitors on the load side of the system. These have to be maintained on an annual basis. All it takes is one years worth of forgetting to do maintenance under the right conditions and the system will go south, like it has in your case.

ME

hot_rod

I think it's the aluminum layer in the Onix is "suppose" to be the O2 barrier. But I wouldn't bet the farm on it

Anybody remember Kitec?

DH123

The mixing valve replacement went well, it was plugged with fine rust like material after 15-16 years.

I need a plan because I don't really feel like getting a jack hammer out to my cement slab.
Short term treating the system with: Rhomar Boiler Chemical Treatment.
Long term investigate a HX.
Will the HX eliminate O2 problem because the onix will no longer make contact with water?

Solid_Fuel_Man

HX and all non-ferrous components on the onix side. Will keep oxygen out of the rest of your system. Will need an expensive bronze or stainless circulator on the onix side as well.

Taylor

hot_rod

This person tried to use one of the Sorbox filter products to clean up a sludge Onix system. Looks like the anode rod inside the Sorbox got dissolved in 6 months, adding to the sludge problem, instead if eliminating it.

kcopp

If the Onix is in a slab you are better off for 2 reasons. Tube in the slab so not in open air and the slab requires lower water temps to run than a staple up. (which was what the pix are from). The higher the water temps the more O2 will go through all plastic tubing...not just non barrier tubing.
You can do the HX route and that will certainly help... all parts in that side of the system will still need to be copper, stainless or brass.
It sounds like you have less of an issue than I have run across.
You would prob be ok w/ Rohmar or Fernox being added to the system.
For systems that are really bad a power flushing tool would be in order. I have been thinking about purchasing one but cant justify the upfront cost at this point. They are super popular in the UK.

DH123

If I coupled the onix to pex, covered the connection with a tape collar that was air and water tight and then brought the pex to a new manifold.

Would oxygen still seep through this connection into the pipe?

Would an on going ph test be the only real way tell if it worked?

Steve Ebels_3

I have a customer with the same problem going on in his system. He's losing 1 or 2 circulators every winter due to getting gunked up.

He has 2 loops, (unknown length) of Onix in s system with a stainless boiler, baseboard through most of the house, all copper piping except about 5-6' near the boiler that is steel.

There are several other piping details that are incorrect on the system but are causing some different problems. I could write an essay about what not to do based on this installation but that's another story...
My main concern is that crud in the system accumulating in the very small water passages in the boiler heat exchanger, (Giannoni type) causing a hot spot and consequent failure of the boiler.

Hot Rod, you mentioned an additive to ameliorate the sludge issue...What particular product are you referring to?

I think I'll direct the home owner to this thread.

kcopp

Hot Rod has forgotten more than I know....
but I have found w all non/ poor O2 barrier systems I have worked on that if you flush the system w water, then drain it out down to 0 psi (thus any water pressure will allow the junk to fall off the sides of the tubing) then re-purge and add the Fernox/ rhomar/ sentinel cleaners. Allow to run for a week. Then flush out again, depressurize & flush. See what you get. if still skunky add more cleaner. then add a good dose of the inhibitor. fernox, rhomar, etc). Most have a way to test to see if you have enough inhibitor in it.
Most of these companies also offer water testing to see what you have in the water. If it bad you may want to purge w/ deionized water.
Caleffi did a great Coffee w caleffi webinar you can see on youtube called digging deeper.

hot_rod

Yep, that is about the best procedure.

Run a cleaner, do a good power purge, either street pressure or bring a purge pump to get some serious flow rate.
You need to flow at least 5 fps velocity to movie solids and particles out.

Then good quality water and a conditioner.

Check the conditioner every 2 years, boost if needed.

Some Onix systems seem to continually sludge, others not at all. I don't have an answer for that.

DH123

My issue was not entirety caused by the unix pipe. I had installed approximately 30' of non-barrier pex in the system which
I have eliminated. Most of the rust from the oxygen entering the system settled in the heart of my heating system. I replaced the auto fill valve, pressure tank, and mixing valve (which was completely plugged).

Now I annually flush the system with water until it feels a 5 gal bucket with clear water, I also soak the mixing valve in vinegar and water over night.

My small system (160' x 3/8" in a slab) is working better than ever and I'm very confident that I can keep it going for a long time, with regular maintenance....

hot_rod

DH123 said:

My issue was not entirety caused by the unix pipe. I had installed approximately 30' of non-barrier pex in the system which
I have eliminated. Most of the rust from the oxygen entering the system settled in the heart of my heating system. I replaced the auto fill valve, pressure tank, and mixing valve (which was completely plugged).

Now I annually flush the system with water until it feels a 5 gal bucket with clear water, I also soak the mixing valve in vinegar and water over night.

My small system (160' x 3/8" in a slab) is working better than ever and I'm very confident that I can keep it going for a long time, with regular maintenance....

I would not flush it annually if you don't need to. Every time you add fresh water you are adding O2 which leads to more corrosion potential.

That was the whole issue with the non barrier or questions barrier tube, constant O2 ingress.

Fill and pressurize the system, add a corrosion inhibitor like Rhomar and let the sleeping dog lie.