If for any reason you have turned OFF the main breaker of your household electrical system, do not simply turn it back ON. In fact in many cases it will simply not turn back on, especially if you have baseboard heaters all on all over the house. Powering the main breaker while all the circuits in the house are demanding a lot of electricity can cause a surge that simply trips the main breaker – making you feel like the main breaker is not working properly.
First turn OFF all the individual breakers, then turn ON the main breaker, then turn ON the individual breakers.
This sequence allows the main breaker to come back ON without any flow of electricity at all. Then turning on each circuit individually only adds a little of load at a time and avoids a very strong surge through the main breaker. You will now discover that your main breaker is working perfectly well.
You say that you have turned the main on and off before without a problem. Was that perhaps in the summertime when there was relatively little electricity being used in the house? Turning the main breaker ON in the winter in an electrically heated house creates a significant electrical surge.
When there is a power outage and the power comes back on there is the same problem of a surge, but your main breaker is already connected. Sometimes that surge blows the power utility’s equipment and the electricity drops out again. It is the power company that gets the surge and you may have heard them asking people to turn off their heaters or ovens until the power comes back on, or notice them turning on one street at a time rather than reconnecting an entire neighbourhood at once.
Using the proper sequencing for powering up your house is important.