Why does my central heating system get so much air in it?

Question

We have an old system with a header tank in the loft. Over the last few days I have bled the radiators many times. However one section:

• Took a few hours until any water got to it,
• Its radiators were then filled with air (I bled them again at this point)
• The next few times the system was turned on, this section heated up as quickly as the rest of the system.
• Now this section is not heating up (I think due to an air lock)

I can’t see any leaks, whenever the pump starts up for the first half an hour the system make a lot of noise. What do I need to do?

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Update:

Closing the valves on the all other radiators, got hot water to the section that was not heating up, but how do we stop this happening again?

Answer 1

Back in the day when I lived in a house with a hot water heating system, I usually had to bleed the air out of system a couple time every winter even though there wasn't any leaks. I just thought that was normal behavior.

Answer 2

I fitted a Spirotech SpiroVent Microbubble dearator to the system; this automatic removes any bubbles of air in the water. As it is fitted as the hottest point of the system just after the boiler, and less air can be dissolved in hotter water, the water going round the system aborts any air in radiators etc, and then the air is removed by the dearator.

Once I had cleared the airlocks from refilling the systems, we have had no problems, so I believe it is working. However ask me in a few years time for my verdict.