There are several factors that may influence the final strength of the coffee.

Below you can find all causes and solutions:

1. The paper filter may have collapsed 
   A collapsed paper filter will cause the coffee to be weak. Always make sure the filter paper is placed correctly.  
   
   
   
2. Use of a wrong paper filter size 
   Make sure you use the correct filter size for your coffee machine. If you are not sure which filter size is needed please consult the user manual.  
   
   
   
3. Using a permanent filter instead of a paper filter
   If you switch from a paper filter to a permanent filter, you may perceive a difference in taste. Using a permanent filter might affect the taste of the coffee.  
   
   
   
4. The amount of ground coffee in the filter
   The amount of ground coffee put in the filter influences the coffee strength. In general, 1 level coffee spoon is enough for 1 small cup of coffee. Depending on your strength preference, you can use less ground coffee for a milder taste and more ground coffee for a stronger taste.  
   
   
   
5. Using another grind than drip-filter grind
   Make sure you use drip-filter grind coffee.  
   
   
   
6. Using the Aroma Control knob in combination with a permanent filter
   Some coffee machines have an Aroma Control knob. This knob allows you to adjust the strength of the coffee to your own taste. If you want to use the Aroma Control knob to determine the right balance between ground coffee and water, do not use a permanent filter. Due to its weight, a permanent filter disrupts the coffee-water balance of the Aroma Control system.

If the above solutions do not solve your problem you can contact Philips Consumer Care in your country.