Bleeding/ heating question

Hello

So my heating stopped blowing out hot air the other day.

Done plenty of research and both pipes in the ashtray are cold.

I've bled from the 3 points and just flowing coolant with no signs of air.

Am I missing something or do u just keep repeating the process until something happens?

Coolant levels has been rising and falling a little which makes me think it is just an air lock but any other ideas of how to get it working would be great.

Coolant was fully replaced a few months ago and it's been working fine.

Cheers
Ian

HAs the dial knob failed, they crack along the shaft or one of the cables come off?