Circuit breaker nuisance trips.
If the cicuit breaker trips occasionally, even when stat and floor test OK, it may be because of in-rush on large heating systems. If everything tests OK, try a QO-HID and QOB-HID High Intensity Discharge Circuit Breakers.
These items are pretty expensive, but they are designed for HID lighting, and are designed for high in-rush applications. Available in local electrical supply store.
If these do not remedy the situation, there might be electrical issues in the house.