radiator not hot after circulator replacement

steamedchicago

I have a Peerless cast iron boiler, feeding what was once a gravity system. Single zone, circulator pumping into the boiler. There was a Bell and Gosset NRF-22, which failed a week ago. I replaced it with a Grondfos UPS15-58. Now, I have a basement radiator that won't get hot.

My near boiler piping is a bit of mess. Coming out of the boiler, the supply Y's off into two 1 1/4 trunks, one serving the front of the house, the other the back. Coming off the branch for the front, there's a tee splitting off a 3/4 line that feeds the not hot radiator. The return for that radiator is hooked into the return for the radiator on the first floor directly above it. The 3/4 supply pipe is not hot past a foot or two from the split.

I assume the problem is that the B&G moved a bit more water, and could get flow into the small pipe. I have the grondfos on high. Is the best alternative to cut into the pipe, and put another circulator to drive water to our cold radiator?

DZoro

Can you bleed the air out of that radiator/ line.
D

steamedchicago

DZoro said:

Can you bleed the air out of that radiator/ line.
D

There's no air. I get cold water as soon as open the bleeder on the radiator, and at the bleed fitting at the tee.

HomerJSmith

Pictures, please. The Grundfos circulator on speed 3 is a good replacement for the Bell & Gosset.

Something else is going on. If it was working before and not now, I would suspect trapped air somewhere in that circuit.

steamedchicago

HomerJSmith said:

Pictures, please. The Grundfos circulator on speed 3 is a good replacement for the Bell & Gosset.

Something else is going on. If it was working before and not now, I would suspect trapped air somewhere in that circuit.

So, I closed the isolation valve on the return from the radiator (which I know was wet, because the stem leaks when its anything but full open or closed) and hooked a hose up to the boiler drain on the radiator (it's the lowest point in the piping, even lower than the boiler). I drained about five gallons of the nastiest looking and smelling water, which sounded like it had a bunch of air in it. The radiator is now heating up. I'll have to check in the next boiler cycle, too, but I suspect that's solved the problem. The air must have been trapped in the vertical pipe between the radiator, and the supply on the ceiling.