We have had this too.
Once it seemed to be caused by a couple of dodgy batches of BiBags - not since.
I am told that the procedure to clear it works, as long as the user is patient and only does what the instructions say, when they say it.
I have only seen it once myself and it appears I can't follow the instructions.
It has been a problem since the very first 5008Ss and I don't think they will solve it, other than saying to follow the instructions !
I don't think there is a particular set of instructions to follow for this one.
Could it be the one where you have to let the concentrate tubes suck in air that you're thinking of as staff and home patients seem to struggle with that for some reason?
I have so far re tubed the bibag side of the machine to eliminate any leaks and also changed the two bibag filters ensuring they are in the correct way. It didn't make a difference. Also tried dropping down to 650g bibags, still no better.
Today's repair involved changing the two 1202 boards on the hydraulics and then all the calibrations that goes with that. Patient was going to go on dialysis later so I'll feed back as to whether that sorted it or not...
Manchester University NHS Foundation Trust