Thank you suggestions. The machine is less than a year old so it was unlikely to have wear and tear.
There are no clips as you suggested. To open the unit,remove the two small wheels at the front, underneath are two screws. So, to enter the unit remove two pairs of screws which are obvious then the 'hidden' screws and that is it!
After cleaning the unit works perfectly! Perhaps my husband can claim most credit the problem, he spent ages studying it before he found the answer.
I hope this information will help in the future, trying to prise 'clips' apart could result in cracking the casing
sorry to give a poor rate but as I have explained trying to get 'clips' apart may well result in cracked casing! Luckily my husband spotted the hidden screws in time.
Thank you time