Loud squealing noise from sealed system – expansion vessel?

[hankhill]

Has anyone ever heard this noise coming from a sealed central heating system? See -

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 partly 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.

 

[Johntheo5]

Is this expansion vessel for the boiler?. A megaflo cylinder has a air bubble, normally. If so, if you switch off the boiler and run off some HW from a tap, is there any noise?

 

[hankhill]

There's no noise when running water from the taps, and the Megaflo is 10 feet away and definitely not the source of the noise. The noise is coming from left of the boiler, where the expansion vessel, pump, and filter are located.

 

[Johntheo5]

So the noise only occurs when the boiler is firing and only heating the megaflo?. What is the pressure gauge showing before and after the pump stops?. Normally the EV precharge pressure should be 1.0bar and the charging pressure (cold) 1.5bar, it should then rise to 1.8 to 2.3ish when the boiler system contents heat up. also when the pump starts you should see the pressure rise by 0.2bar or so.
If the EV has failed the PRV should lift at a pressure of 3.0bar and system will need constant top ups

 

[Madrab]

Is that the filling loop mains valve on the supply you are playing with that changes the noise? If so it's may be that ISO valve that's passing.

Disconnect the loop hose from the top of it and see if it's passing water or if the check valve at the other end is failing.