Hi @Florence,
Thanks for posting this here - hopefully I can provide some helpful information.
As mentioned above, Volatile Organic Compounds otherwise known as VOCs are odours that including cooking, burning fuels, perfumes and cleaning products.
These VOC omit as a gas, which is detected by our Purifiers and are drawn into the machine passing through the filtration system to remove it from the environment. This gas decays at a steady rate as the air in the room is passed through the machine and clean air is expelled - this process can be affected by what is called ‘Off gassing’. This is where a source is producing the gas at a rate higher or the same that equals the machines purification. Read a full explanation on our What is off gassing and what causes it? article.
As the machine has been successful in reducing the reading, even after some time, it would suggest to me that the source decreased the rate - as the spike came back, it could mean that something within the home is producing the reading.
As this is the second machine you’ve had, I do not believe there is a fault in production, more so that something locally is causing the reading. The importantly thing is to locate what in the home is producing the gas. This can be done through trial and error. Changing cleaning material, moving the purifier to a different location in the room and/or checking for points when outside air can enter the room are only a few suggestions.
With the above in mind, wiping the sensors on the machine will remove any material on the surface - please following the advice under our Cleaning the sensor. This will help ensure the machine is working optimally.
Thanks,
Stuart