Yes you are right. There do have 2 elements which run in parallel so 1 half may be at fault.
To replace isnt thats diffecult really on these. You need to take off the bulged cover on the back and the right hand side panel.; Then from there you will see the heater element on the back. Take it off and then undo the wiring on the right hand side. Then from there you can replace with new heater unit.
If you need anymore info just get back to me.
Many thanks - It sems quite straightforward - I shall investigate before wasting money on a new one.