repairing bathroom wall heater?

I have a bathroom that has a small heater (electric) set in the wall. It's a guest bath, and I have company coming, so I checked it. It doesn't turn on. Last time I tried it, it was fine, but that was two winters ago, I think.. Someone said it's a breaker, but none are in the off position. Unfortunately, this is a partly old house seems to have a lot of quirks wiring-wise, and there is more than one breaker box, the one that seems to be the biggest of three,is in the "old" part of the house. Of course, very few of the breakers are labeled. Is there any way to figure out if it's related to that if there are no breakers obviously tripped? I hate to turn each breaker off and run around to see what it turns off if there's an alternative. It's a big house :).
Thanks.