Hi,
I have a gas boiler heating both floors of my house. The configuration is such that both floor return pipes combine and go thru the single circulator and then into the boiler. Earlier this year the boiler failed to circulate the 1st floor system. The repair guys first thought it was the control valve failure, but later found it was working, Another guy said it was electrical failure and replaced the thermostat. System seemed to work after the replacement, but it failed again overnight with the same symptom (1st floor not circulating). Later it was diagnosed as an ailing circulator and it was replaced. So it was the ailing pump issue right from the beginning, though I am not sure why the ailing pump was able to circulate 2nd floor, but not 1st floor. This system has been generating a lot of metallic air noise all along and I could hear the water flowing in the pipe all the times. I did flush the whole system in the past and also before I turned on the boiler this month and I could see air bubbles came out. Unfortunately now there is a bigger problem. The system generated a very loud pounding sound I believe whenever the circulator first started to circulate water on either floor. The sound was loud, like the pipe pounding heavily on something, or sometimes the radiator rattled violently. It is very annoying and worrisome. The air vent has been broken (leaking) in the past so I closed it completely. I tried to bleed upstair radiators, but in one radiator I only saw a couple drops of water and then no more water coming out, nor air that I could detect. There are 3 heating loops on the 2nd floor and I think I have heard the pounding sound generated on any of them. In other words, the sound could happen at a couple different locations, I believe. It looks like whenever the pump circulates it generated some sort of momentum energy and rattled the pipes heavily (air?). How should I go about fixing this problem? Thanks in advance.
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