Boiler noises and air

[JohnBailey]

My CH has always needed me to bleed one radiator regularly, I don't seem to have any leaks just air getting in when the heating is on. I don't think it happens when it is just HW on.

Does anyone have any ideas what might cause it?

Also, and I don't know if they're linked, while the water is part way into getting up to full heat the boiler seems to make train-chuffing type noises for quite some time.

 

[Agile]

To enable the resident experts to have a better chance of giving the best free advice, I suggest that you could give the make and model of boiler and say if its an open vented or sealed system!

Tony

 

[JohnBailey]

My system is a vented system (Y plan?), with Glow worm space saver boiler (installed in 1981), 3-way diverter valve, grundfos pump, potterton controller/timer and horstman programmable room stat.

Trying it just now the noise was most obvious when it was heating HW only (I got it wrong earlier). When getting hotter each 'chuff' (like in a steam train chuff-chuff etc) was accompanied by a tap or knock noise that sounded like air movement in the region of the boiler, but at nearby radiators it sounded like a metalic tap-tap-tap. With HW-only, the boiler cut-out fairly soon, I guess as it got too hot. The cylinder has been in about 7 years.

Over the years the system has made less or more noise at various times, but it has always managed to get air into the system. The bathroom rad (nearest to pump/mid point valve) is the one that gets air, probably going down to half-full in a month or thereablouts.