Ususally when you get an IC or IU displayed on your board it means you have communicaiton errors with a certain speaker. The best thing to do is if it is a repeat problem or one you can make happen. Start by turning all the speakers at the master station to off. If the problem doesn't happen, turn 1 speaker at a time on unitil the problem starts. That eliminates your other speakers. Usually that speaker has to be replaced. If you have any other questions you can email me at ragerandsons@sc.rr.com or visit my website at www.ragerandsons.com. hope that helps, Greg Rager Rager & Sons Inc "Authorized Nutone Serivce Center"