I have a Dyson Pure Cool purifying fan. For a little while it has been telling me the air quality, in particular the PM10 and PM2.5 levels are severely bad. In fact as bad as it can measure. A reading of 999.

Looking at the history in the app it hasn’t dropped at all over the last few days so I knew it wasn’t an accurate reading.

What is PM 2.5 / 10?

PM stands for Particulate Matter or Particle Pollution . PM2.5 and PM10 are minute particles present in the air.

Particulate matter is a complex mixture of soot, smoke, metals, nitrates, sulphates, dust water and rubber etc



In my case some PM material must have got into the sensor port causing a false reading. All I had to do was to carefully clean the sensor port.

  • I switched off and unplugged the fan
  • I used a hover with a hand held attachment to suck up any dust and other material from in and around the sensor port
  • Powered the fan on and within a few seconds the readings returned to what I would expect.

If you are looking at the LCD screen on the front of the fan the sensor ports can be found around to the left side on my model at least.

Don’t jam anything in there at most a soft bristle brush! I just used a hover from the outside that was enough in my case