I have a Rhreem gas heat pump which I tried to turn on today for the first time this season. It doesn't turn on, even though it worked fine last winter. The thermostat clicks and the unit "hums" but the blower isn't turning. The A/C and fan work. It does have propane. I checked the fuses and they are good. Before I call a service technician are there any other simple things I can check for?