Jonesey
From the experience with both of my machines, you seem to be on the right track.
The machine senses wire breakage by the lack of rotation of the brake roller. ( the one with the yellow neoprene sleeve on top ), or more specifically, irregular rotation of the brake rollers.
The two most common cause I've found is that the carbide pinch rollers might be dirty, or the neoprene on the brake rollers have a groove too deep for adequate grip, and they stall for a moment.
Remember, they are on the powder brake's shaft and they provide the necessary tension to the wire.
There are also a couple of other, less common causes I've found.
The obvious: Improperly wound spool. It will cause enough fluctuation in the wire speed that it'll alarm
Pretension motor ( the one holding your wire spool ) has an electric brake clutch and a motor. It is completely dry, and over time can get rust built up inside the clutch as well as the bearings.
If that one snags, it'll also cause a momentary stoppage of the wire.
Also, if you have the wire chopper, worn ceramic inserts in the chopper sometimes pinch and stall the wire. The feed rollers stop for a second, and you get the wire break message.
Turn around roller in the lower head might also have a deep deep cut in the V-groove. If that roller is dirty or the bearing is shot, then the deep groove will stall the wire.
So, I would recommend taking apart the lower assy ( just 3 screws in total ) clean the rollers, guides, guide seat surface and the ceramic guide tube.
If you have the brush that came with the machine, clean the long tube all the way through in the lower arm. Otherwise fish a straight wire through it to push out the built up ( it will be there !!) deposits.
Clean the water/wire separator.
Clean the carbide pinch rollers. Best done with acetone soaked towel, but make sure you don't get much onto the plastic.
You may also use a fine sandpaper while the rollers are turning ( just put the machine into Thread mode, the rollers will spin endlessly and you can scrub them completely )
Change the ceramic inserts in the chopper
Either flip around the neoprene brake roller, or if both sides are used, put them on a lathe and turn them just clean to make the groove disappear. You can get 3-4 lives out of them that way.
All of the above should take you less than an hour to do, I do it every 2-3 weeks or so.
If you still get the error after the cleaning, take apart the break assy and the spool motor with brake and clutch. Clean it and you can gently lube the bearings and bushings ( NOT THE CLUTCH!!! That you can clean with alcohol! )
Good luck, let me know how you make out.