My house has a hot water system with two pumps. The first loop is original to the house: radiators w/ iron pipes. The second is copper pipes with heating through aluminum fins. Each loop has its own Bell & Gosset Little Red Booster pump, thermostat, and Bell & Gosset Flo-Control valve. Lately when the second pump starts up, the pipes start clattering horribly all the time that the pump is going. I don't recall offhand if the first pump may also cause the clattering. Both pumps are pretty new. I have managed on one occasion to stop the vibration by opening one of the radiators, but that seemed to be a fluke. There doesn't seem to be a reliable way to stop the vibration. I don't know where to bleed the second loop. I think the Flo-Control valve for the first loop is stuck open. The expansion tank was emptied fairly recently (2 years ago). The noise is getting to be rather annoying.
