Air quality will not improve - Severe 999 reading showing | Dyson Community

Air quality will not improve - Severe 999 reading showing

  • 9 August 2023
  • 4 replies

We have an Dyson Pure Hot+Cool Advanced Air Purifier which we purchased in 2019 and has been working fine. Lately we set it to cool at night and everyone morning we come down and the fan is at full power. We’ve also been away for a week and for the whole week it was at full power to clean the air. We recently replaced the filters from the 2 piece set to an all in one part as supplied by Dyson. 

As you can from screenshots it doesn’t seem to improve the quality. What can be done to stop it always being on high and the air quality not improving. I have a feeling it might be a sensor or something as nothings has changed in our home. 

Thanks for any help. 



Best answer by JamJam 9 August 2023, 13:59

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4 replies

Userlevel 5

I think this is a blocked sensor. If it continues, a reset might be best.

Here are two links that should help you.

My machine/App shows a 999 Severe reading, what do I do? | Dyson Community

'Power Cycling/Restarting/Resetting' the air treatment machine | Dyson Community


I agree. Most likely some dust or dirty in the sensor port. Vacuuming the ports is a safe bet. Once you’ve done it, switch the unit off for 5-10 mins. This should reset the sensor port. 🤗

Userlevel 6
Badge +8

Hi @crookesa,

As others have said, this is most likely an obstruction of the sensor ports by some fluff or debris. Wiping it with a soft microfibre cloth, or vacuuming it using a soft dusting brush, should resolve things.

Viewing the purifier from the front, with the LCD screen facing you, rotate the machine counter clockwise 45 degrees. The sensor ports are located on the left hand side, just above the perforated filter housing.

Let us know how you get on!

Hi everyone,

thanks for the tips and the hoovering of the sensor slots seems to have worked and it’s working as expected now. 

for some reason the app isn’t working so just trying to fix that now as I have to repair it and the connecting part is hanging but at least it’s not like a wind turbine any more. 

cheers to all.