New Dyson Hot+Cool Purifyer doesn’t show VOC, is it broken?

Hello, 

I have a new Dyson Hot+Cool Formaldehyde purifyer and it seems the VOC sensor is not sensitive enough. I suffer asthma and therefore I own two Airthings Wave air quality monitors. The AW monitor went from VOC 76 to VOC 620 in a room where I have closed windows. The Dyson app shows VOC 0. 
I tried to vacoom the sensors but there was no change.

I have opened windows. It reacts well to the PM values. It seeems that the NO sensor is not sensitive either, because outside there is NO 9 but inside NO 0 on the Dyson app and there is almost same air as outside now.

I made a test putting a bad smelling item next to the sensor and it reacted, so the sensor is not broken, just not sensitive enough.

I would like to know, it I manually increase the fan speed, does it clean the gasses more? Or is it necessary for the machine to measure higher VOC itself to start to destroy the gasses?

I increased the fan for maximum for 30 minutes (with the windows closed) and there was no change in VOC in the room, the level have been slowly going up without interruption.

I am very happy with other Dyson products I own like vacooms but this seems an issue. What to do? Shell I return it? For the price I could have two Philips purifiers that clean particles but I wanted something that cleans gasses too.

Thank you for help,

Marketa