Hi all,
I’m experiencing something with my Xiaomi Air Purifier Pro that I thought I should share.
Yesterday I felt that my eyes started itching and the aqi in our apartment started to rise.
Rising is not strange, but more than twice of outdoors aqi seldom happens. After running around with my air monitor (AirVisual Pro) looking for the source I suddenly had a spike of aqi 1700, in the middle of our apartment.
Turns out it was the Air Purifier.
I turned it off and on once and the fouling greatly reduced (1200, still terrible).
Then I turned it off for 5 min and then when I started it again it was initially quite good (aqi 20, should be 0 though), but after running for a few minutes it reached aqi 330.
So it seems the problem is heat related. I would guess a failing bearing or motor.
If anyone has any other ideas what might cause this please reply to this thread so I can suggest them to the technician 
Now fortunately enough we still have 17 days warranty left, so we contacted Xiaomi and they will send a technician today to come have a look.
I’ll come back and update this post with the results.
Update
So the technician just concluded the particle sensor is faulty and needs replacing.
Obviously this can not be the reason the machine fouls the air but the technician claims so and left to fetch a new sensor.
Update 2
Summary:
Technician changed sensor, problem persisted. Since sensor works and air flows from the machine the machine is deemed fully functional. Next we have to argue with Xiaomi. Update will follow.
Rant:
Today the technician came and replaced the sensor, it did not go well.
Obviously the guy had no idea how to change the sensor and hence had not brought appropriate tools, he only knew where it was. But after a few minutes and a lot of force and bending using an electrical screwdriver he got it out and popped the new one in. For future reference, it’s just mounted with double sided tape, pull it straight out.
Unsurprisingly the problem persisted once he turned it on.
Next he wanted some smoke or air pollution to test the sensor, so I fried some leftovers in some oil and he held the machine over the counter which of course sent the aqi soaring.
With this test he showed me that the sensor works. (this was never in question from our side which we made very clear the first time he came.)
Next he held a napkin over the outlet to show that there was air coming.
He concluded that since the sensor works and there is air coming there is nothing wrong with the machine.
He then put the old sensor back, but did not replace the damaged adhesive.
Next my wife got in to a heated argument (in Chinese) with the guy and then he left.