Can't move water or air between supply and return. Clog?

LegendsCreek

I was hoping for some advice before I call my boiler company. I fired up the oil boiler to my guest house for the first time this season. One zone works fine (baseboard radiators) and the other zone (buderus panel radiators) will get the radiators hot, but then the return line at the boiler is cold. Eventually the heat stops at the radiators.

I shut valves on the supply and return, and then tried pushing water through with a garden hose. Tried pushing water in the supply, which should have come out the sillcock on the return. Tried running the water through the return so water would come out the supply, same thing. No water is coming out either side and the valves are wide open. I tried air also and its filling with pressure, then when I remove the air, its squirting out a bunch of black water but not pushing air out the other side.

Everything worked earlier in the year before we shut the system down for a few months to do some work in the boiler room. Neither the pump, air or direct water pressure from a hose are pushing water through the loop.

Any advice? Very worried.

LegendsCreek

Oh I should also add that I bled air from the buderus radiators directly. Not much came out.

MikeSpeed6030

Just a guess: when you shut down the system last spring, and if the zone in question was isolated from the expansion tank, a vacuum might have been pulled, causing a pipe, fitting, or a radiator to collapse, pinching off flow. What type of pipe does the system have? (Copper is weak under a vacuum, and PEX isn't too great either.) Are all the lines accessible for external inspection?

Using compressed air, as opposed to pressurized water, for testing piping systems is dangerous. There is much stored energy in compressed air, even at seemingly low pressures - and if a fitting should break loose, it could become a missile. I am aware of a fatality when a pipefitter removed a valve bonnet from a system that was, unbeknownst to the fitter, pressurized with air for a leak test.

When all else fails, you may need to open up the system, one place at a time, and pinpoint the area that is clogged.

STEVEusaPA

This is a pretty common problem in the fall-first time using boiler.
Might not be clogged. Might just need a proper bleeding/purging/filling. I would also make sure the circulator is working, the expansion tank is ok, and there are no leaks.
I recommend to call your tech. It's almost impossible to tell you all the different ways to do this, or what to check, but a qualified person can size it up pretty quickly and start troubleshooting.

LegendsCreek

Thanks for the help Mike & Steve. I solved the problem. It had to do with the thermostat valve on the actual Buderus rads. I am pretty pissed, but pretty relieved that it was just the dials not being set property and I don't understand how with the 3 buderius valves not fully open, the circulator on the actual boiler cant still pull water through the system. The way I designed the radiators when I installed them was so that everything was fed off of a main loop, so the supply and return should still circulate even if 1 of the radiators is closed.

Very confused and very relieved!!