hb48054gb/02 when the temp is set to 250 it heats up for a few mins then the display changes to 150? i have found the cooling fan motor very stiff but no power to it im not sure on this mod what temp it is activated is it that the oven isnt reaching temp to start the fan or is the pcb detecting a fault?dont fancy splashing out on a fan if theres another problem any ideas???? 😕