My Creda Concept Solarplus model 48339 cooker timer display illumination disappears, and can only be seen if you press hard onto the lower/front display panel. I presume that the printed circuit board is cracked, or is making a poor connection. Are spares still available for this part?
If its an LCD display, it may be recoverable f you are prepared to strip the unit down and clean the 2 'rubber' strips that connect the pcb to the 'glass' display screen AND the 'glass' surface that touched those strips. Use alcohol (meths) as cleaner and don't touch any of the surfaces with your fingers. The strips are actually flexible connectors.
Don't start until power is removed. Usual disclaimer -all at your own risk!