Dekema 3001

[marakidental]

I have a Dekema Austromat 3001 that does this..... Warning beeps will sound before the high temp is reached and will SOMETIMES continue to the set high temp, or sometimes stay at the temp that it starts beeping ( usually 5-8 degrees below set high temp),or sometime drops in temp. What could be wrong? Thanks

 

[Nenad]

Did you calibrate furnace recently