vitcas bread oven door thermometer problems

[slen916]

recently fitted one of these to my oven door and it will only read as high as 100c,dont know if its faulty or ive put it on wrong...any ideas

this is a pic of the back of the door
shop.vitcas.com/vitcas-pizza-bread-oven-door-thermometer-500-c-676-p.asp