Rattle when circulator shuts off

Quick background. I have an oil fired forced hot water system. This fall the system would not produce heat. The technician from the oil company told me it was the flo-check valve. I replaced that only to find it was the circulator. I replaced that as well. The Flo-check and the circulator are both from Taco (previous ciruclator was gurndog?).

After the boiler there is a low water cut-off, pressure reliefe vlave, flo-check, air bleeder, expansion tank then circulator. House has only one zone.

There are ball valves after the ciruclator and on the return so I was able to isolate the radiators while I did the work and did not drain the whole system.

Ever since I did this work I hear a rattle in the radiators when the circulator shuts off. It happens every time, it is only a few cycles. I suspect the flo-check. The screw on top of it is all the way in. The noise is barely perceptable when near the system but seems to resonate in the radiators (old cast iron stand up radiators)

Also, may be conincidenc but worth mentioning... about 2 months after I did this work my expansion tank started leaking at the seam and had to be replaced as well. I checked and the system is running at about 17 PSI.

Any ideas?

 

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Lucvky you!


Despite the fact that you didn't drain down the system, I would suppose that your noise is caused by air trapped in a radiator.

You will usually find a tap that allows air and water to be drained off each radiator. I'd open the tap on the noisy radiator and drain off water until any possible trapped air has had a chance to be removed. That might take 15-20 minutes.

Your problem might be something else, but I'd start there.

 

thanks, I expected this response. Thing is I can't identify which radiator it is coming from. I kind of hear it through out the house. That is why I suspect the source of the noise is elsewhere and is resonating in the radiators. It definitely sounds like the source is a metal chatter. I fully expected to hear it loudly coming from the flo-check but that was not the case, there is sounded muffled. Of course that doesn't mean it is not the source.

I've never bled radiators before. A few questions.

Should I do them in any particular order? Start on the second floor?

Best way to avoid a puddle/mess?

Most of the valves on the radiators have been painted many times and have not been opened in a long time, most of them are only stems with no knobs. I did open on of them a few weeks ago. the wooden knob broke in half (explains why there are no others) leaving only a small nail through the stem. After I let some water drip out (did not see any signs of air) I closed it. I then had a drip from this valve for a few weeks.

Thanks for the response.