My Bunn nhbx-b leaks water when brewing coffee

Here is the manual for your unit:
Bunn NHBX Use And Care Manual

The reservoir is not removable.

lift filler led and remove 2screws on top of reservoir
Then remove 4 screws that hold the reservoir on an you should be able to lift it off

lift filler led and remove 2screws on top of reservoir
Then remove 4 screws that hold the reservoir on an you should be able to lift it off

The manual for this coffee maker can be found at this link:
http://manualheaven.com/assets/bunn-nhbx-b-contemporary-coffee-maker-manual.pdf
While the manual does not contain repair instructions, it does have some troubleshooting tips to follow if your coffee is not staying hot.

It sounds like you might have a problem with the water tubing. If you will call Customer Service at 800-352-2866 we will be happy to assist you with this issue.

Please give Customer Service a call with the model and date code. If the machine is 3 years old or less, it will be replaced with a new machine. If it is older than 3 years, it can be exchanged for a reduced price.

I work for BUNN. Here's a link to the manual for your NHBX-B
http://www.bunn.com/pdfs/retail/usecare/41756.0000_STX_NBX_U_C_English.pdf

before plugging in place your empty filter basket in the coffee maker and place a pot under it. Slowly pour in two pots of water using the pour pitcher. Now you can plug it in. it'll take 15 min to heat up first time . when you brew your first pot leave your water level a little short,because the water will expand (only the first time)