I had the same problem with my lervia oil filled radiator
which would not heat the rad. turned out that the thermostat which is located at the top inside the control panel was burnt out and was not visible from view. to gain access to this area unclip spring at base of control panel, remove flexi cover from around outside section of rad. prise off plastic cover at top of rad and remove two screws which allows the control panel to separate from the rad. you will then see the thermostat which is fixed to the top of the rad. and connected to control panel by two wires. it was this part which was burnt out.replaced by my local heating electrician...best of luck.
JOHNNY R P, January 2013