OWB , underground piping

We got an SOS call last week for'' low return water temp'' . Now this was previously an OWB, open system. It's a coal fired plant now, but the 300' of piping is original from way back .

We pressure forced water , one leg at a time , pushing from the house end to the opened coal plant end.
I collected the sediment from both supply and return . Both held about 2 coffee cans of crud each.

No real story here, it all worked out fine, but maybe it can help someone.

I suspect it was from years of the open OWB .

Hi Dave - it doesn't have to be an open system to have crud in it, although open systems are the worst. My system used to have a wood boiler in it, and the previous owner would let the PRV blow in mild weather. This allowed a lot of oxygen and minerals to get in the system. When I replaced a lot of the old piping with pex tubing, I noticed that the pex turned black inside after the first season. This was from debris inside the cast iron radiators, and probably from the oil boiler also (was connected at the same time as the wood boiler). Last year I ripped out most of the old system, and set my EFM up as the only boiler. I used a product called Fernox F3 to clean up the system and it seemed to do well, but just a few weeks ago when I started the system up the screens in my mixing valves got plugged with black crud.

I ended up cleaning the system with Tri-sodium-phosphate, per the directions in an old Weil McLain manual. The water that came out was as black as used motor oil. I had to power flush all of the zones to get things clean.

I refilled the system with fresh water, and 8-Way boiler treatment from Rectorseal. So far the water has stayed a violet color and the screens are clean. Something else I have noticed - my EFM used to "kettle" after a long burn (sounded like water boiling in a pot). It no longer does that. I am not sure which part of my cleaning process removed the minerals from the boiler, but all is well!

Hi Rob , a quick update, after 24 hours from flushing the pex under ground feed and return. The family noticed the change when taking showers this morning. I stopped by later and they have 4 deg temp difference from supply to return.

I would hate to see what's hidding in my boiler

Dave, do they have any plate heat exchangers in that system? If so, you may have to flush those from both directions to get them clean.

Rob R. wrote: ↑

Wed. Oct. 27, 2021 4:26 pm

Dave, do they have any plate heat exchangers in that system? If so, you may have to flush those from both directions to get them clean.

Rob , I checked on that yesterday , the old exchangers were removed . One house still had low heat, ..... that turned out to be a simple air pocket . The loop that had most of the sludge still had low heat on their DHW , that was a mixing valve , we turned it up and it looks like now i can get them to bring the coal boiler temp back to a more efficent range.

It's much easy'er to ''fine tune'' if it's a system that you live with.