I have awoodburning fireplace in a house I just purchased and I cannot figure out how to turn on the blowers for it. It has what looks like a thermostat that has two dials and a glass tube of some sort. One dial has number rangeing from summer setting to 250. the other is labeled with the word "dif" and numbers of 15,40, and 65. I have tried moving these dials or levers and nothing has caused it to come on. I check the breaker for it and it tested ok..can someone tell me how to get this blower operating with a fire burning in the fireplace ? thanks