You can check the sump hose/ filter first for blockages – accessible through the small cover plate on the rear of the machine. If your machine is connected to a sink trap be sure to check that the washing machine outlet hose and the nozzle it fits to are clear.
If no blockages are found, then it could be the pump or control PCB at fault. It is advisable at this point to call an engineer. You will risk wasting money if you buy expensive parts you may not need. Click the banner below for an engineer in your area.
Always – ensure power is off before any inspection.