source of rust in radiant system with buderus radiators

EternalNoob

Seeing an excessive amount of rust in the water with this radiant system, supplying half the house with staple-up and half the house with radiators. The rust is now seriously restricting the flow through the mixing valve, and I'm at a loss as to what the source could be. Photo of the mixing valve is AFTER I cleaned it. Have not used glycol or anthing but am considering it now.

• using oxygen barrier pex for all the in-floor staple-up, double checked this
• have 2 buderus panel radiators which i'm not that familiar with, supposedly are made of stainless steel, but it's hard to locate specifications for these things, this is the only thing that's significantly different compared to other systems i've worked on.
• only part in the system not made of stainless copper or brass is the cast iron taco pump

hot_rod

is it barrier Pex? Where is the expansion tank connected into the piping? Does the system hold pressure with the fill valve turned off, no leaks?

dko

Other than pump and expansion tank…

Stainless steel can rust. It is rust resistant, not rust proof. Stainless steel is an iron alloy with other elements to make it what it is. We call non-magnetic stainless steel austenitic not non-ferrous. Between ferritic, austenitic, and the numerous grades of stainless steel with their oxide layer can all eventually rust. The type and grade of stainless steel used for the spring on the taco mixing valve and your pex manifold is unknown.

Corrosion inhibitors in your closed loop system can help extend the life.

Also realized you didn't post what kind of boiler it was. If aluminum heat exchangers, will require a more specific pH level.

The buderus panel radiators are steel, not stainless steel. so are all similarly looking white panel radiators. They all claim "premium quality" steel though!

But I guess that all really wouldnt matter as the actual cause would be oxygen. Which would be why hot_rod is asking the important questions

EternalNoob

thanks guys.

• Definitely oxygen barrier pex.
• That the buderus radiator is actually made of steel makes sense, feels like the suspect element to me.
• Expansion tank is on the cold side of the WH. It is the potable type (white not grey), not sure if that may have something to do with it's performance? maybe it's factory-set pressure is too high? Could be the culprit? If exp tank not performing could cause low pressure on the upside of the pump allowing air in the eliminators? Could be an easy part to swap out and see if it makes a difference.
• Presently not pumped with primary/secondary, single pump, considering doing P/S pumping and eliminating the mixing valve.
• WH is an 80 gal stiebel Eltron heat pump water heater set to 149 deg F. Yes i'm aware that these are not typically used for radiant, but this is a very small and well insulated house in california and it covers the btus pretty well. WH is a glass-lined steel tank.
• Don't think the problem is from old / warn out parts, as everything is only a year old. Had problems with this system from the get go, made some posts about it a year ago. Continuing to feel like I don't know what the heck i'm doing.

EdTheHeaterMan

So I have a question that sounds kinda dumb… is the HP water heater used exclusively for space heating? If you are using the HP Water heater for both heat and hot water, then you have an open system. Can't have the iron pump or the steel rads on an open system.

Assume you know this and you are using the heater for space heat closed system only, so I have another question. Did you run out of Ox barrier PEX at the end of the last loop? If yes did you just grap another 10 feet of what ever PEX was available to finish the job? Just that 10 ft of PEX without an O2 barrier can allow enough oxygen in to cause your problem.

Just spit ballin' here.

Mr. ED

psb75

Wait a minute…you're using a heat pump water heater to heat your house?? The water heater uses heat from the house to make hot water. Seems like you've invented a perpetual motion machine.

You've comquered the laws of physics. Many have tried but you finally prevailed. Quick, file for a patent!

EternalNoob

* HPWH is located outside, so I'm staying safely within the confines of thermodynamics principles. The only perpetual motion happening here is my regular return visits to the house.

* HPWH is devoted to radiant, separate WH for DHW. The fact that the expansion tank is the potable type is unrelated.

* It is unlikely but possible a small length of non barrier PEX was added. The staple-up was installed by the homeowner and i was very adamant about choosing oxygen barrier PEX and checked the label myself, but he is a handy guy and does have some PEX elsewhere in the house so it's possible he used some scraps from elsewhere. I will ask if that's the case. Really don't want to go digging through the insulation to check it.... If I suspect that is the case then perhaps glycol is in order.

kcopp

Maybe add an inhibitor but NOT glycol…. that will only make the issue worse .

Clean and flush the system. Fill and flush w/ Deionized water. Axiom has a nice filter.

WMno57

How much iron is in the water before the water is added to the hydronic heating system? Well water can have a lot of water soluable iron. It will be clear when it comes out of the tap, but will oxidise and percipitate out if you leave a glass of it on the counter for a day.

hot_rod

It is always a good idea to test you water that you fill with. Putting inn hard, aggressive, high iron water will compromise the system from day one.

If you don't test I would buy good water to fill with.

EternalNoob

The water source is tap from the city of Oakland, exact same water as i've seen in other trouble free radiant systems in Oakland, so i think a high iron content is unlikely, but that is an interesting thought.

Derheatmeister

Is this Glass lined Stieble Etron Accelera ?

How old is the Waterheater and did you check the anodal operation…

15.6 Protective anode
The flange of the electric booster element is equipped with a
protective anode that protects the appliance from corrosion while
it is connected to the power supply. The protective anode is a
maintenance-free impressed current anode.
If a fault code in the display indicates that the protective anode is
faulty, proceed as follows:
 Remove the controller of the electric booster element.
 Check the protective anode connector and its wiring.
 Refi t the controller of the electric booster element.

One of the problems with Electric anode is that you will not see if they are depleted …If your Glass lining is compromised the waterheater WILL CORRODE even with "Good Water"or Deionized Water.

Most compromised glasslined waterheaters that we see are installed in basements or transported very roughly,

BTW the manufactures warranty states that this waterheater shall not be installed outdoors…Impropper System fluid and expansion tank sizing is also addressed in the warranty,