Diplomat oven fan temp not heating up

Hi all. I have an oldish 8yrs+ Diplomat that has done me proud, but the other day, i turned on my fan at 180deg c as per usual, but it did not reach the temperature. It was hot, but definitely not hot enough. The fan is working as i think it should be, as i used another fan cooking setting and it worked as normal ( picture of an upper horizontal line, then below it the fan symbol, and below that, another horizontal line, lines indiciating oven). That function is the fan with added elements for faster cooking and it worked fine. So a bit puzzled. I have not touched nor never really touch any clock settings, timed, auto etc. Only time i touch the clock is for clocks back and forward every year. Thanks for any info !
The manual i have for it has the model nos. ADP 4600, 4602, 4610, 4612, 4613 on the front cover