Dyson Purifier Humidify+Cool Formaldehyde Air quality detection strange - Should I repair it?

Dear community,

I’d like to ask before I send the device to service.

We have it for some 4 months but from the beginning I observe strange behavior regarding the airquality detection.

It’s not about it doesn’t detect a bad airqality (it’s 99.9% problem VOC). But after detection it almost never purifies / solves the problem. What helps always is a restart (power cable out and in). Examples:

• I tried to put something smelly near the sensors. It detected and the line went yellow. So it works.
• The purifier is running and it detects something in the evening and the line goes yellow, ventilation 8-9 pretty loud. This doesn’t change until the morning. So it is loudly running the whole night but the airquality is not better (at least he thinks so). Plese don’t think there is something smelly in the night. no! It happens also during the day when the flat is empty and we are away.
• What always helps is a hard restart. So imaging the line goes yellow and it’s starts a hard purifying. In 5 Minutes I take out the power cable and put it back. The line is green and stays green. 
• In the case theree pruifying doesn’t make the line green in hours, I do the same restart and again, everything is green.

I have to ask. Does the power cable restart purify the air????? For a so expensive device I would expect more. What can be wrong ?

PS-I tried to suck the sensor are with vacuum cleaner. It didn’t help.

thanks a lot for any tips or help.

Marek