Has anyone ever heard this noise coming from a sealed central heating system? See - https://youtu.be/1IGz-HjDJPo
The noise reminds me of air escaping from the neck of a balloon. It happens almost daily, for a minute or so, normally while the hot water (Megaflo) is on (heating is off as its summer). I can stop the noise by opening the tap used to top up the water pressure, as in the video.
I strongly suspect that it’s the expansion vessel that has failed; the plumber on the last service did have to top up the air and it’s been making this noise ever since. I was just hoping for confirmation from someone that has heard this before.