Black discoloration in pex

Al Corelli_2

Just worry about it if it turns red.

Scott Lind_5

I'm going to have the boiler water tested but knowing I need to tell them what to test for - beyond ph, hardness, chlorides....

Any idea what might be causing the inside surface of barrier pex to discolor to dark gray/black? This is a 2-1/2 year old system with in-slab pex, underfloor pex and standing cast iron raditors, brass manifolds, Upnor and Rehau pex.

System orginally was just in-floor and I used NoBurst for several months before house was completed. Flushed those loops with water before completing system and filling.

No auto-fill and have only had to add water when blowing out the in-line strainer I installed to catch any loose rust form the old rads and for an initial leak in a couple of the rads caused by the sandblasting when they were restored.

A symptom that may or may not be related is the failure of 3 pressure switches on the boiler - this is a Viessmann Vitodens 200.

Thanks,

Scott Lind

Ross_7

it's the cast iron radiators

It's the cast iron radiators in the system. I have the same problem with my pex,but it hasn't harmed anything.

klaus

Absoultly the rads

It is certainly the cast iron Radiators in your system causing this. You have water going over cast iron, what happens? Fortunatly you most likley have an air eliminator and have minimum oxygen entrained in there. The result is a black coating that you'll find in the pipes, pumps, boiler, radiators, etc. Take apart a century old hydronic system and you'll see the same thing. This coating actually protects, I've been told, the inside of the components of your system. It's not hurting anything. If your water's okay, just leave it be.

John Starcher_4

Every Pex....

....job I've ever done in a system with cast iron (boiler OR rads) has done this. NO worries, mate!

Scott Lind_5

Thanks!

...for all of the quick responses guys. Good to know I don't have some sort of anerobic bacteria growing in there.

I'll probably still do a water test to check for other invisible water quality issues that might (not likely?) explain the multiple switch failures.

Have a great Labor Day weekend,

Scott

Ted_5

A side stream filter would help

The color is not a problem, but particals floating can cause the pressure switch problem. Look at adding a side stream filter. HeatLink offers one that is 55 micron and does a great job of cleaning a system out.

Ted

Brad White_194

Side Stream Filters

I use Neptune filter feeders, which run me about $400 or so but for an older system retrofit, it is a good investment. Insert bags come in, IIRC, 50, 30, 20, and 5 micron efficiencies.

Even the 2-gallon size has 3/4" tappings so I reduce down from my 1" main size and use it to filter all the flow rather than side-stream.

I toss in a few rare earth magnets (there I go again... and the water becomes clear as you can imagine.

As Al Correlli said, worry more if it turns red (active rust) rather than magnetite. I would add though that this free iron can bond to stainless steels which is why I like to scavenge the stuff out.

radmix

black in tubing

I have done several jobs that have had high temp loops such as baseboard and low temp loops such as slab radiant all off of the same primary loop and have noticed that the pex on high temp loops turned black and the low temp pex loops remained clear. the color starts right off the supply manafold and continues to the return. It is my opinion that it is the temperature of the water that makes this color not rust.