If your dishwasher isn't draining properly there are a few simple quick-fix solutions to check before calling in a repair specialist.
Check your dishwasher's filter. The filter is usually located underneath the lower rack on the floor of the machine.
To clear the filter, remove it gently and wash it in your kitchen sink. The filter usually unscrews in much the same way as a plunger or a petrol cap would. Once removed, it can look like a variation on any of the below filters:
Clear the filter of any detritus; including food wastage, flecks of plastic packaging and broken glass or ceramic shards. Do not run a dishwasher cycle straight afterwards (you run the risk of flooding). Instead, fill up a jug of water at the tap and poor this into the floor of your dishwasher with the newly-cleaned filter in place). Check to make sure that the water drains away without incident, and if it does, run a quick wash through your dishwasher to check that everything is in good working order. Stay close to the dishwasher while doing this, so that if the dishwasher becomes clogged once again, you can switch off the dishwasher at the socket and prevent a flood.
Have you recently installed a new waste disposal unit? Dishwashers often share the same drainage pipe as waste disposal units, and if one becomes clogged the other will often be affected too. If the pipe has become blocked, you can try clearing it yourself using a specialist drain cleaning product. These usually involve pouring a corrosive liquid down the drain (via the dishwasher's or waste disposal's filter) and leaving it for 24-48 hours until the blockage has been broken down and cleared.
If these two quick-fix solutions fail, it may be that your dishwasher's pump has broken; the pump is the mechanism which extracts water during the washing cycle, and fixing it involves calling out a specialist. The pump is a delicate piece of technology, and it is best to leave this up to the expert.