Integrated Bosch dishwasher – recirculating pump change

Morning,

Changed the whole circulation pump entirely apart from the pump housing. When i run the machine the impeller seems to be jamming the motor. Deassembled and reassembled the pump countless times and no luck. Is there a trick I’m missing when screwing the impeller into the pump? The spacer is the correct way round and the impeller will not screw any further.

Any tips greatly appreciated,

Thanks

Tim