I have an older Bunn Coffee Maker

Question

My grandparents has an older Bunn Coffee Maker and they love this thing so much they had another one given to them and it was new and they wanted to continue to use there own So when they make a pot of coffee it does not keep it warm they can drink it staright out of the pot and its not warm they have to pop it in the microwave to warm it up what could be wrong with this.????