Black tar / ooze emerging from radiant system

RemoteRoads

Looking for some diagnosis assistance. We live pretty remote so local assistance is virtually non-existent.

Radiant floor heating unit 10+ years old attached to direct vent propane water heating tank. Yesterday we woke up to the smell of hot plastic and it looks like something black has bubbled out of the air vent (guessing its an air vent, our unit is clearly a discontinued Eco-King and I can't find anything online about how it was setup).

When I cleaned the black stuff off the vent it started leaking excessively and the screw vent cap was too corroded on the inside to be fixed so I know at least I will have to replace that. Ended up having to turn off the radiant system and cut the flow.

Here is a picture of the whole setup with the propane water heater tank to the left and the radiant reservoir at the bottom.

Aside from replacing the air vent does anyone have ideas what caused it to burn and bubble black in the first place? It looks like there is also a bit of black corrosion on the heat exchanger. We've never replaced the glycol and the liquid is a light tan/pinkish color. If my memory serves it was either clear when we built or the lightest shade of pink.

Any ideas would be greatly appreciated.

Lance

Just can't tell from the pic. If wires involved it overheated the materials to a point of liquification. If just leaking, its PH reacted with the plastic. Color could be mold related? Clean it up and monitor it. Some materials do not interact with other chemicals well.

hot_rod

glycol turns to a thick brown or black substance when it goes bad

Is the tubing barrier pex for heating use? Non barrier pex will compromise the glycol quickly, especially if you run it hot, over 120g

Probably time to flush, fill with clean water and a hydronic cleaner, flush again and refill

Do you need to have glycol in the system?

Steve_166

Looks like your "goo" issues are on the heating loop side of the flat plate heat exchanger. That would be the side with the glycol you said was in the system. Antifreeze is very corrosive, so the manufacturer adds a corrosion inhibitor. Problems start when antifreeze starts to get old - that's the cause of the "goo" at any air vents or leaking valves/fittings. Both freeze prevention and the inhibitor start to decrease over time. Cryotek makes strips for testing the quality of both in your system. Draw some heating liquid off and check it. You can just add inhibitor if necessary but with a small residential system, I just do a good flush and add new glycol. Moving forward, check your quality annually.

Good Luck

Geosman

Yes, I've seen this in the past. Typically if an inhibited propylene glycol is added to well water, softened water or even city water, the minerals in the "potable water" may compromise the inhibitors in the antifreeze that are intended to maintain a neutral and non-corrosive solution. It's highly likely that the antifreeze has gone sour and compromised the needle valve inside the air vent causing a slow seep that has turned black with time and heat. When flushing the system you might flush with your tap water. Add a good dose of blue food coloring and monitor the volume of fluid discharged until the blue color comes back around and the fluid becomes clear again. This is the volume of distilled water you will want to flush the system with before adding antifreeze if the system has any zones that may be subject to freezing temperatures. Any antifreeze added needs to be carefully calculated based on its concentration and the desired freeze point. Also inspect the Axiom glycol feed tank and clean any residue from the tank. I find that if propylene glycol is added to an Axiom tank in a concentration less than 30% it can over time start to grow a bacterial mold which is also black and not what you want introduced into your radiant system. Consequently I find adding distilled water only to the Axiom tank assures a clean mixture for my systems and if the tank runs low, I know there is a small seep out in the system which must be addressed Small seeps in radiant floor systems can often be sealed using a product called Loop Conditioner. It requires recirculation under pressure but has successfully sealed several leaks I've encountered in systems installed way back in the 1970s. The following source is for geothermal loops but the solution is also marketed for sealing leaks in PEX tubing, and RV piping as well as hot tubs and swimming pools so it has been in wide use for quite a while.

https://geohydrosupply.com/geoloop-leak-seal-geothermal-loop-conditioner/

hot_rod

unless you have access to DI water, I would buy premixed glycol 30- 40%

But you need to used compressed air to get all the flush water out. I keep a gallon of full strength in case you need to boost a bit from dilution.