My glow plug light has stoped illuminating, now cold starting is difficult. I have owned the car for 6 years and the light has always illuminated, even when warm for a split second up untill a month ago. The Citroen hand book also states that the glow plug light will illuminate in warm conditions for a split second. I have fitted a new pre heat relay box and Citroen have fitted a new temperature sensor, but the light and glow plugs will not pre heat. The glow plugs work ok on post heat with the engine running. Citroen are now telling me that the light and the pre heat function should not operate untill the temperature is -15. I would be very greatful for some advise regarding this, thanks.