Reply To: Circulator pump in hot water central heating causes hum throughout hou

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#287773
Harold Kestenholz
Participant

Unfortunately, Sylvan is only marginally able to understand the written word, so he gets half the meaning of this question. Evidence:
1. The circulator makes no noise while you are standing next to it; therefore the couplings are not making noise at the circulator. As he suggests, check the alignment. If the circulator does have a coupling, that is a way to move the impeller forward and back if it has some play in the bearing, but it is not a fix. It is a clue to change the circulator. That was my first answer.
2. Gravity systems circulate water on their own, even when you don’t want them to, if you have nothing to stop their flow. Sylvan’s suggestion to put valves on the radiators would stop and start flow. This would help the situation by controlling heat in the rooms, but more important to your question, it would slow down the natural flow of water in your system to help your circulators.
What most young plumbers don’t know today is that a pump should not be driven by water coming into the inlet or be totally unloaded. In other words, if the pump does not have a back pressure against it, the impeller bearing gets a varying load, accelerating wear and making noise. Clue: your statement about frequent pump failure.
Manufacturer experience with this problem recommends the smallest circulator that will move enough water and a balancing valve 10 pipe diameters from the circulator outlet to set up a constant head pressure against the impeller.

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