When using Preen for Carpets PowerShot or Preen for Carpets OxyAction it causes brown stains on the areas where it is applied. Why?
This condition is called browning and it is caused by over-wetting carpets, either with a cleaning product or with water alone. It is the saturation of the carpet that may allow moisture to reach the carpet backing or even the underlay. This discolouration is not usually permanent, a professional cleaner should be able to remove the stains.
