Central Heating noise waking me up!

Recently, our Central Heating has been waking us up in the morning when it comes on. It makes a "wailing banshee" kind of sound. Before I call the elders of the chuch to exorcise the house, I though I'd see what you all might recommend.
I checked the header tank about a month ago had found it to be empty, the ball valve stuck closed. That's fixed now, but clearly there was more water needed in the system - I have been bleeding our bathroom radiator regularly over the last few months.
We had a British Gas engineer round the other day who replaced the main CH pump. He said that was (most likely to be) the problem, having worn itself out when there was no water available to pump, but we still get the banshees coming back. The boiler itself sounds a bit like a kettle when it starts (high-pitched hissing) - it never used to. Typically, when I tried to show the engineer, there were no noises. I don't mind the usual expansion/contraction tapping sounds, but I don't like being woken up with the CH coming on!!!
I'm not entirely sure where the noise is coming from - it usually only lasts about 2 minutes, and I haven't crawled out of bed to listen to each and every part. I am pretty sure that the noise is being sent round the system and that it's not the radiator in my bedroom that is at fault.
Any ideas?! Thanks, Aelx
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Sounds like air in the system to me.

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PJO wrote:

So what's the best way to get rid of it!? If the air isn't getting to a radiator, bleeding won't help....
Alex
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If you're only bleeding the system from one radiator, then you're not bleeding all the systems properly. You will have to bleed everything on the system to make sure you're getting all the air out, and that includes the boiler itself. You will find the boiler has, or better have, a bleed point on the highest part of the pipework for this very purpose.
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Do you have thermostatic valves on the radiators, these can whissle and moan as they close. It may be that the pump speed is too high, sending the water round the radiators too fast, try turning the speed down one notch and also balalancing the system, see the FAQ for this group.
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I had a whistleing noise from the rads and did the above and that sorted them fine. However, that was only once the heating had been on for a while and the TRV's were closing, if the noise it at the start then it's probably something else like air in the boiler.
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Big Phil wrote:

No TRVs on the system. This morning, I jumped out of bed to investigate. The boiler itself was making some noise, and I discovered that it stopped and restarted 3 or 4 times in a row. After it stopped, changing the boiler's thermostat made no difference whatsoever, so it had probably cut out. My guess is that there is an air lock in the boiler that causes problems at the start - after a while, the pump has managed to push enough water into the boiler for it to work properly... I now have to work out how to get the air out of the system. There is a valve directly above the boiler, on the "flow" side - I twisted it this morning, but there was just water coming out. I will have to check for any other valves...
I would love to know how the air gets to the boiler that causes these problems - which are only when the system starts up in the morning. Perhaps there is some problem with the boiler itself??
Alex
PS Where's the FAQ for this group located, please?
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You could try turning the pump speed up to max for a couple of hours. This might help shift any air.
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Over the past year, my central heating was also making a real racket when it started up causing the vertical pipes to rattle. I thought the pipes had just come loose from their fixings (which they had).
However, last October the pump failed. The engineer came to replace it and the new one is perfectly silent. He said that the pump failed due to air in the system and that the central heating piping was incorrectly installed causing air to be pulled into the system. This is maybe how air is getting into yours. I'm afraid I can't remember which pipes were incorrect. He did say that the pump's life would be reduced unless the fault was remided.
Regards, Rob.
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