Hydronic Heat Rust issues:Thermolec B model

[Woody PME]

Ok, I’m hoping this is the category for this thread but if not please steer me in the right direction:

I am having issues with corrosion in my hydronic floor heat system. The system includes a Thermolec B model electric boiler. Now I’m pretty mechanically inclined but have little experience with these systems. Several weeks ago I noticed a big spot of rusty dusty residue on the mech room floor and followed the trail up to the Spirovent Micro Bubbler that had apparently been spewing the rusty slurry for some time. I shut down the boiler and began investigating. The water throughout the system has darkened and is contaminated with the oxidized material. I’m sure this means flushing the system but I need to locate and replace the source first. My first thought is the boiler tank is deteriorating. Am I on the right track? Does this mean replacing the whole unit or just the tank? What else should I be checking? I’m open to any feedback, suggestions or advice here.

Pics Below:

I live on an island and while there is a HVAC contractor here I haven’t had much luck with them in the past and have little faith in their quality. Before I call someone from off island to come out ($$$) I want to figure out what the hell is going on. Thx!

 

[Dana]

If there is a leak in the system and fresh water is being added at some slow but steady rate to keep the pressure up, all iron components in contact with that fresh, oxygenated water will rust, including iron-body pumps. Without oxygen replenishement "dead" heating system water is not going to be corrosive.

The PEX tubing in the system has to be an "oxygen-barrier" type too, since other types of PEX are oxygen-permeable, thus oxygen from the air will enter the water via diffusion through the pipe walls to create corrosion issues. If standard potable-plumbing PEX was used, that is a likely source of oxygen feeding the rust problem, but the PEX is probably not going to be replaced.

Sometimes there can be galvanic corrosion issues, where dissimilar metals meet in the system, but that seems unlikely here.

A magnetic filter can keep flakes/chunks of rust from getting into things if the corrosion levels are really bad. Replacing the pumps with stainless or bronze body versions can eliminate that source of rust, and replacing the black iron & galvanized pieces with brass, copper or bronze plumbing can eliminate those sources of rust.

I have no idea if there are corrode-able ferrous metals in the boiler's heat exchanger tank- does a magnet stick to it?