Mixed hot and cold rads and sounds like air in heat coil?

[layttom]

I have Vaillant Ecomax with megaflow. Hot water works fine but during the recent cold snap want to crank the heating up only to find a mix and match of radiators giving out heat. I did recently top the pressure up in the system and bled it. Find all top floor working well most of the middle floor and some on the ground floor only. As I have been observing this over the past four days I noticed that the hall radiator last night was hot and had not been for the previous days and others cool that had been warm (not hot). I have taken the cover off the boiler to listen to the noises coming from the pump and believe the sounds are coming from the heater unit. After letting the system cool and the start up the noise was quite extreme - surging and gurgling. Once running have the normal roar with regular surging noises of different pitch. Are the issues inter linked and easily remedied. Have checked the radiators for air again but none yielding. All radiators bar two have stats.