A CRJ900 flight crew responded to ANTI-ICE DUCT warning and caution messages by returning to their departure airport. Later believe warnings to have been false.

Narrative

The temperature was below 10C and we were in IMC so we had the wing and cowl anti ice on. While climbing out around 8000 feet we had an ANTI-ICE DUCT warning message that went to a ANTI-ICE DUCT caution message after a couple seconds. I called for the ANTI-ICE DUCT checklist in the AOM. I continued the climb to the assigned altitude; while noticing no ice accumulation. We were above the layer and in the clear at 10000'. I continued to fly the plane and communicate with ATC. The First Officer completed the checklist; and we no longer had any message indications. I asked him to contact Dispatch. Dispatch informed us to return to our departure airport. I told ATC that we wanted to return due to an Anti-Ice Duct caution message. They gave us vectors to return. I then asked the First Officer to notify the Flight Attendants that we were heading back because of the fault. I then transferred controls with the First Officer to give the passengers a brief; then transfered the controls back. We completed the checklists and briefed the approach. During the descent for the approach we entered icing conditions again. We turned on the wing and cowl anti ice switches on. Again as before we had an ANTI-ICE DUCT warning message that went to a ANTI-ICE DUCT caution message. I called for the ANTI-ICE DUCT checklist in the AOM. When we turned the wing anti-ice switch back on we received no more warnings or caution messages and the system was working correctly as we checked the synoptic page. We were also not accumulating any ice. We completed the approach; landing and taxi to the gate with no further incident.