I am in the UK. I have an existing closed (pressurized) heating system with a boiler downstairs and the rest of the works + hot water tank in the cupboard upstairs.

Problem: when lots of radiators are open (they have electronic valves) + the hot water zone is on, the non-return valve emits a rather annoying "droning"/"buzzing" sound, but at other times it is perfectly silent. The valve was replaced recently on the assumption that it could be defunct, but the problem did not go away.

System schematic: Heating system schematic

I suspect that air pushed from the radiators might get in the section of pipework highlighted in red and becomes trapped there, creating some sort of airlock, and leading to the issue I am experiencing. Is this a reasonable assumption or crazy talk? Would fitting an automatic air vent there help?

  • Your last question should be asked as a question of its own. While it's all related to your heating system, they're separate questions.
    – FreeMan
    Apr 3, 2022 at 16:26
  • Makes sense. I split it off
    – ADEpt
    Apr 4, 2022 at 21:46
  • 1
    Please write up an answer of what you did. That will make it easier for others in the future to find an answer and help them out.
    – FreeMan
    Apr 5, 2022 at 13:47


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