Hi Mcd,
Check the following:
1 – filters in the machine (obvious)
2 – outlet coupling – if the machine is coupled to a sink outlet, check that joint – it can sludge up.
3 – the syphon stop valve is part of the fill hose and is therefore irrelevant to your current predicament.
4 – I assume the machine has not movedin its 3 years. This is quite an adequate period of time for a “crushproof” drain hose to collapse if nipped!
Few thoughts there, if none of this sorts you out either check in Directories for a local UKW engineer, or stick your post code in here and someone will help you.
Regards,
Penguin45.