I use an R2.
I sometimes take off the chaff filter between roasts to vacuum it out and clean it.
When I do so, I see a message on the screen saying “Low Exhaust Fan RPM”. is this an error or a warning? How should I clear it?
When you took the chaff colector it releases the safety button and comands the exhaust fan to stop (that’s why it shows “Low exhaust Fan RPM”), be mindful to put it back as soon as posible to avoid overheating issues
Thank you. I notice the message remains sometimes even after carefully replacing the chaff collector.
Should the message disappear by itself in this case, or are there steps I should take to notify the Bullet to check the chaff collector status?
It clears itself, usually takes about 10 seconds. I think it’s controlled in the firmware of the roaster. When the fan is disengaged, I notice the power drop to 0. I think it’s a great feature though, and fixes the issue if you accidentally don’t seat the chaff filter enough to engage the fan, before this update you wouldn’t really know unless you’re visually checking the impeller or you end up seeing smoke or condensation dripping from the machine.
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I just ran into this Low RPM message mid roast 
I cleaned my chaff filter / collector out completely before the roast and maybe about 15-20 roasts ago I had cleaned the impeller fan and assembly as well.
I’m currently still running the “Cool Roaster” mode so I can’t test anything out. I’m thinking I might need to clean the impeller fan again in order to get this message to clear? I will report back if this fixes it or not.
Anyone else had issues mid roast running into this error message?
Update:
I think I figured it out.
I believe my chaff filter was non installed perfectly the last time I cleaned it, therefore the safety switch was being disengaged during the roast occasionally. When you remove the chaff filter from the bullet there are black fins that align your silver metal piece to the plastic’y outside, and that was my issue: it was not flush.
Roasting another batch as we speak, so far so good.
Some other users were chatting about similar things in this thread: Chaff container fitting