Rear Heated Windscreen Delay

Hi guys, this is my first post.



I have a Laguna II DCI and have a strange issue with the rear heated windscreen. When i start the car in the morning and press the rear windscreen heater button, the orange light comes on. However it takes 20 minutes before the heater jumps into life (i hear the quiet click as it turns on). Its the same every journey. Any simple way to solve the issue?



thanks in advance