AIR TRAP ?

steve_25

I HAVE BEEN REPAIRING THIS OLDER 2 ZONE HYDRONIC SYSTEM FOR SOME TIME. HOUSE WAS EMPTY FOR 2 YEARS, SYSTEM FROZE. I REPLACED ALL CONVECTORS AND REPAIRED/REPLACED MOST OF THE BASEBOARD.NO PROBLEM PRETTY STANDARD STUFF. PIPING RUNS THRU ATTIC SUPPLY / RETURNS, USING MONOFLOW TEES TO FEED RADIATION. PUMP IS ON RETURN SIDE OF BOILER. BOILER AND NEAR BOILER PIPING DID NOT FREEZE. HOWEVER I INSTALLED NEW CIRC. AND ZONE VALVES AND AIR VENTS WHERE NEEDED.  FIRED BOILER... GOOD ! BLED ZONES, GOT EVERY THING TO HEAT EXCEPT END LOOP OF BASEBOARD 8'. THIS IS A 3/4" LOOP WITH A DEVELOPED LENGTH OF APPROX. 35'. THERE IS AN AIR VENT AT THE TOP ELL OF RETURN IN ATTIC. THERE IS A BLEEDER AT TOP ELL OF SUPPLY, THEN PIPES DROP DOWN 8' TO FEED BASEBOARD LOOP. I CAN'T GET THIS LOOP TO HEAT. I INSTALLED BLEEDER ON FAR END OF LOOP AND NEAR END OF LOOP. WHEN I BLEED I GET HEAT BUT I CAN'T ESTABLISH SUPPLY/RETURN FLOW. I'VE TRIED EVERYTHING, BLEED, NEW AIR VENT, RAISED PRESSURE. THERE ARE PURGE AND BALANCE VALVES ON LOOP, DONE THAT. THIS ONE HAS ME STUMPED. ANYONE OUT THERE WITH A 2 X 4 ?

kcopp

Turn off...

the Caps Lock for starters....  The bleeder needs to be further down stream after the baseboard. It is still air locked. The piping sounds crazy. You may have done better just starting over.

Big Ed_4

Down Flow Monoflow

Your problem is not air .It is flow... A down flow mono-flow needs the proper flow to force the hot water down into the radiator .… Each radiator uses two vanturi tees ... Get rid of the zone valves and use an independent circulator ... Something like a Taco 0010

Steve Whitbeck

mono flow

Put the pump on the supply with a mono flow loop. It will work a lot better.

also you need a pump with more head on a mono flow system than a paralell loop.

Harvey Ramer

Try putting a couple 90's on the main loop between the feed and the

return of the baseboard that isn't heating. Mono flows don't work by themselves. You have to have enoungh resistance on the main loop to make the monoflow work. Or you could decrease the pipe size between the fee and return.