Noisy immersion cylinder when heated by central heating boiler

[Leo Maggs]

My IDEAL central heating boiler is over 30 years old and had been 'kettling' for some months. My plumber drained the system, refilled it with some kind of sludge remover, drained it again and refilled with the required anti-corrosion stuff. The boiler is now very quiet. BUT, when set for 'hot water only' the copper cylinder in the airing cupboard makes a very loud slurping, belching noise. We have bled the system several times but the noise persists. My plumber is stuck for an answer. Any suggestions?

 

[John Wilkins]

have you bled the rads or hot water coil? there should be a bleeding point around the cylinder

 

[PowerFlushUK]

Possibly put an air separator in the airing cupboard.

Any idea what kind of copper cylinder it is? Does it have a data sticker on it? How old is the cylinder?

 

[Leo Maggs]

Yes. All rads and cylinder bled several times.
The ‘belching’ noise starts only after the pump has been on for about 5 minutes, which leads me to wonder whether the ‘belches’ come after a build-up of pressure from the pump releases a blockage, which then returns when the pressure has been released.

 

[Leo Maggs]

Cylinder is a HERCAL, manufactured in 2004