OK - did you start with cold water? If not - that may be the problem. Found these basic instructions for Bunn coffee maker - probably smaller size that what you have but can't be much different. Hope they help you.

Modeled after commercial coffee makers, the Bunn GR10 Home Coffee Maker can brew up to 10 cups of coffee in just three minutes. It utilizes a water reservoir to keep water hot and on standby, always ready to brew a pot of piping hot coffee quickly and without the normal wait time associated with other home brewers. How does the Bunn Home Coffee Maker GR10 do this? When you first set the Bunn GR10 up, you add up to 10 cups of cold water to the water reservoir and turn the power switch on. It will take about 15 minutes to heat the water initially. This water will stay hot and ready until you go to brew a pot of coffee. To begin brewing, you simply add cold water to the reservoir, which then displaces the hot water already in the system. This hot water is sent to the filter basket instantly where it diffuses through your freshly ground coffee. Afterwards, the cold water you just poured in will be heated for your next round of coffee brewing. And if you're planning to be away, just flip the Vacation switch and the heating unit won't continue to maintain the water temperature in a ready state.