Help ---can't bleed my combi system

[scrumpyjack]

Is there any special way to bleed this sort of system It has a greenstar heatslave 12/18 boiler and the whole lot is 7 mths old. recently I have had to bleed the rads and I can't seem to get the air out.
I used to bleed my old system starting with the rad furthest from the boiler but it doesn't seem to be working for me Is there a special order to bleed combi systems rads in?

 

[bengasman]

if you can't get any air out, what makes you think it needs bleeding?

 

[scrumpyjack]

if you can't get any air out, what makes you think it needs bleeding?

Yeah sorry What I mean is that I get the air out but next day when the boiler first fires up I can still hear air bubbling in the rads.
When I get home the system has been off so I do it again and there is more air. So, back to the question, is there a certain way it should be done to make sure I get it all out

 

[idealnumber1]

do you have any leaks?

 

[swidders]

have you repressurised the system before, during and after you have tried bleeding it?

 

[mogget]

Yeah sorry What I mean is that I get the air out but next day when the boiler first fires up I can still hear air bubbling in the rads.
When I get home the system has been off so I do it again and there is more air.

Is the system adequately protected with inhibitor?

 

[bengasman]

when run on very low pressure, the boiler could suck air in through the aav when it cools off completely

 

[scrumpyjack]

There are no leaks-I have always kept the pressure between 1 and 1.5 bar and there is inhibitor in the system.
I checked the pressure when I bled the rads yesterday and noticed that the pump was running at max speed. I switched it to low speed and when the heating came on it was much quieter and seemed to heat up just as fast.
Today I went round all the rads again and there was no air in them.
Could the speed of the pump have caused the noise and air