A common problem found with the DC08 and DC11 cylinder cleaners is a notable loss of suction that seems to remain despite cleaning the filters. If you have such a machine and have noticed that the performance has dwindled, you might also detect a dull 'pop' approx 1 - 2 seconds after the appliance is started. This is the internal by-pass valve operating which is there to protect the motor from becoming starved of air. Instead of using just the suction air from the vacuum hose, the air is now coming into the machine from around the body. The problem lies within the pre-motor filter yellow casing which, unlike the older Dyson models, has a double low micron membrane which has a tendancy to clog once the micro-dust gets inside. This is great news until you actually want to wash the dirt out. The pores, once clogged are so efficient that even water cannot pass through them. A simple test is to first of all, fill the yellow filter with water (with the blue sponge removed) and hold it up. If the filter is clear, the water will run away, if not, the water will either slowly drip away, or may not even drain away at all. If you also hold the filter up to the light, you will see daylight through it if it is clear, and the extent of the blockage if not. There are only really two things that you can do. Either scrub away with an old toothbrush until you can get the water to run free through the filter, or replace it. Dyson DC08 pre-motor filter.