Expansion Tank failed - twice

don_205

I hope by asking this question that I do not offend anyone...how can 02 be a issue with copper pipe and black
iron on a closed loop system?

Other then having a leak that he does not know about and the water feeder just keep adding water.

Jeff Lewis

gone through 2 honeywell tanks in 2 years

I have a radiant floor system, powered by a Munchkin boiler. We love it! But, I've gone through 2 expansion tanks in the two years the system has been operating. Both tanks formed a pin-hole leak and had to be replaced. The leak appears to be about where the bladder would be connected to the tank wall inside the tank (of course, I'm guessing on that -- I didn't cut it open). Both tanks are Honeywell TK300-30-1 models.

Hard to believe that I got two bad tanks in a row. Could there be something corroding the tank from the inside out? Any suggestions on what to look for?

In all other repects, the system has operated flawlessly.

- Jeff Lewis

Undonaassesee

oxygen

Try a potable tank-take the charge down to fill pressure(12 psi) and it will hold up against the micro-bubbles carrying the O2

steve_196

expansion tank

Those pinholes, i believe, are the result of the manufacturing process. When we had to replace one, we always said another one built on a friday. Microbubbles in your expansion tank? help me out here.

don_205

How it mounted

Is the nipple up or down?

Paul Pollets

Oxygen diffusion

I'd bet that you have non-barrier radiant tubing installed. The O2 diffusion can cause extreme corrosion and eats holes in the sides of exp. tanks. It will cause premature failure of the boiler. Installing a potable expansion tank will help. but not fix the problem.

If so, you'll have to separate the tubing water from the boiler water with a flat plate heat exchanger. The Taco Mixing Block is ideal for the fix, with built-in pumps and FPHX in one module.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Unknown

The good thing is

it is eating your tanks. The bad thing is what is the next weakest link in your system. If you install a super lined tank the water will eat the next iron rich material in the system. The cause is water chemistry and mainly not removing the oxygen from the water. The cure usually not so cut and dry.

Undonaassesee

micro-bubbles

Entrained air in a hydronic system-Not so sure about the "manufacturing process diagnosis" Steve

Rod Kotiga

We always install the tanks as high as possible on our built panels so that they don't end up as a sediment trap in the system. Installing the tank under the main air vent is common but I like to put a tee under the main vent and a drain valve under the tee and use the branch of the tee to pipe up to the tank. I only use a potable tank and let the pressure out to 15 psi. Glycol will help with your o2 problem too. Oxygen rich water make up instead of a Glycol feed tank will kill tanks sooner than later as well.

Rod

Doug_7

Key Questions - Jeff

Don asked a key question - How is the tank mounted - Is the nipple up or down ?

Is this a closed system or is it an open system with constant fresh water make-up ? What is the water source ?

If this is a closed system have you considered chemical treatment of the water - such as an oxygen scavenger ?

Doug

Jeff Lewis

You guys are a great source of information! Thanks for all the quick responses.

To fill in some info -- the tank is mounted underneath a SuperVent air eliminator, so the water side is up and the air nipple is down. It is a low point in the system, so I wondered about it collecting sediment.

The system is closed, but I wanted to avoid chemical treatment if possible. A local installer said that using chemicals can be as much trouble as not having them, because keeping the proper balance can sometimes be tricky.

I have two air eliminators -- one where the tank is connected near the radiant pump manifold, and one near the boiler piping (but at a high point). Sounds like maybe I've got an O problem anyway.

lee_7

What type of piping? Pex, copper, black iron?

billtwocase

exspansion tank

Try a genuine Amtrol extrol tank. There continues to be alot of garbage knock offs out there. been thru the Ventrite, Combu, Sparco, Therm X, and so on. You might get just out of warranty with them. I've seen tanks mounted in every location and position. Never found that to have any effect on the life expectancy of a tank. Also size the tank to the system.I prefer 2 30's where a 60 might be required. Just my 2 cents. peace

mark ransley

A guess, but maybe right, is to heat the system up real hot to remove latent oxygen. Contact systems techs.

Mark Eatherton

Mark...

If in fact the issue is oxygen diffusion through the walls of the tubing, it is compounded at higher temperatures. Not a good idea to heat things up.

To the HO, if in fact it is an oxygen diffusion issue, and you have other non ferrous components (cast iron, steel) in the system, they too are degrading and will eventually fail.

As has been pointed out, your options are limited. You can

1. set a heat exchanger to isolate the non 02 barrier tubing from the heat source, or

2. Use all non ferrous components in the system, or

3. Use a chemical corrosion inhibitor that must be checked and updated on an annual basis.

Get back to us and let us know if it is in fact non oxygen barrier tube. You can't tell by looking at it. You have to find a brand name or number. It all looks the same from a distance, but there is a BIG difference.

Unfortunately, many unqualified installers don't realize the need for oxygen barrier tubing, and go under the premise that if oxygen can make it in, why can't water make it out. Nothing could be farther from the truth, and unfortunately, consumers like your self get burned in the process. If you ignore it, your system WILL go away.

ME

Jeff Lewis

tubing is NOT O2 barrier

Well, I figured out that the tubing is NOT an oxygen barrier type. Maybe that is the source of my problem. Most of the system is copper, but there is black pipe at the boiler. Everything seems to have the appropriate dielectric unions to make the transition, but I suppose the oxygen in the system is going to be a problem for me. Great!

- Jeff

Mark Eatherton

THAT is a BIG problem...

Now that you know, treat it appropriately.

ME

lee_7

Copper and black iron not the issue, it is the non oxygen barrier piping.

Mark Eatherton

Rust never sleeps...

and neither does oxygen. And NO ONE should be offended by ANY question. We're here to learn and teach.

No such thing as a silly question, just silly mistakes made by people who are afraid they will look silly for asking a question. That is probably the main reason people use false identities here on the wall. They don't want their fellow work mates to realize how little they really know about hydronics:-) Either that, or their employer told them NOT to post on the Wall, and they do any how...

Anyway, with non oxygen barrier tubing, it is not an issue with non ferrous metals, like copper and brass. It IS an issue with ferrous metals, like steel and cast iron. The expansion tank failed first because it is the thinner metal (probably THINNEST metal) in the system. The steel pipe is degrading at the same rate, but won't show signs of burn through until much later in the game, but I guarantee you that it WILL show up eventually, unless preventative measures are taken.

Dissimilar metal connections in a closed loop system with non oxygen barrier tube will degrade the lesser noble metals (steel) MUCH faster than a true, oxygen free system. Even with dielectric unions in place. In fact, it is my experience, and the experience of others, that di-electric unions CREATE more problems than what they are worth. The best dielectric connection between dissimilar metals is the use of yellow brass, except the tree huggers have required the manufacturers to get the lead out, so now they start leaching water right through the walls :-(

Stainless steel is also neutral to both metals, but small bore threaded fittings are rare as hens teeth and about twice as expensive.

Now there, see, that didn't hurt, did it? And I didn't offend anyone that didn't need it :-)


ME

don_201

I'm lost

Jeff said that he has copper infloor emitter not non oxygen pex pipe.

I've been to many copper floor emitter with steel copper pipe that were over 50 years old and never had issue with o2 unless there was a leak.

I've also seen system with non o2 pex or that rubber hose they use to used and seen what it could do to a steel boiler in no time.

jim dowling_2

The older the water in the system the less corrosive it will be. Put plenty of valves on the new boiler when installed, so when you have to change a water part on the boiler,you will loose as little of that old precious deoxigenated water as possible. My boilers expansion valve has not been drained in 10 yrs.

Mark Eatherton

Where did you see that Don?

He said it is mostly copper and black pipe, and I guess I assumed that he was relating to the near boiler piping.

I didn't see in any of his post where he talked about copper in floor emitters, but if in fact it is, then you are correct, O2 diffusion through a metal pipe is NOT an issue. It is only an issue with plastic pipes.

ME

don_201

I'm sorry

Thats what I get for leaving my reading glasses at the shop.

Carry on.

Steve M_2

2 air eliminators?

I caught that you said you have two air eliminators on the system. That may be your problem right there, one may be actually sucking in air depending on where it's located. You should only have one air eliminator if you're "pumping away" from the expansion tank and no auto air vents as well.

Fellow wallsters, correct me if I'm wrong.

Jeff Lewis

Yet more info - pipes, tubes, and air vents

Just to clarify a couple of things:

The boiler is piped with black iron, which connects via dielectric unions to copper for distribution to the radiant heat manifolds. The radiant system uses copper pipe to carry the water to the sub-floor, where it feeds through plastic (and I use that term in its ultimately generic sense) tubing. The tubing is described by the Mfr. as Poly PXC tubing, and I have confirmed that it is NOT an oxygen barrier tubing.

There are two air vents on the system. One is located at the boiler, and it is a simple vent (similar to a Honeywell FV series). The other is a Honeywell SuperVent located near the radiant heat manifold.

There are also 2 expansion tanks, both TK300-30's. Again, one is near the boiler, and the other is attached to the bottom of the SuperVent. NOTE: Only the tank attached to the SuperVent has failed (twice), but I assume that is because it is mounted very low and the other is mounted very high, just on the boiler fill line.

OK - that should give you more to talk about! Please, keep it up. This is a great education for me (I mean that -- really). I wish I would have known some of this stuff 3 years ago!

Thanks - Jeff L.

jim dowling_2

You never mentioned If glycol was in system, or if extrol tank #30 is mounted correctly, horizontal or vertical. note: there is no comparision between an extrol and an expansion tank when considering longevity, only the cost.

Jeff Lewis

no chemicals

No glycol, just water.
Tank is mounted vertically, with air-fill nipple downward.

Steve M_2

That explains it

Having non barrier tube explains it as some guessed. At least you don't have to replace the whole boiler if you replace the black iron with brass. Replace iron pumps with bronze and use a potable expansion tank. I haven't worked on a Munchie in awhile and can't recall if the nipples off the heat exchanger are black iron and replacable. If the installer didn't know about the problems with non barrier pipe I'd guess they probably didn't pipe it correctly either, i.e. Primary/secondary.

Unknown

Say you isolate

the non barrier tubing from the boiler with a heat exchanger .

Since it is non barrier , would you still have continual air problems in the zone ?

Steve M_2

yes

Yes, you could do that as well.