Gas and Oil Home Heating Furnaces - Setback Thermostat

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Handyone
11-10-01, 05:40 AM
I installed a programable thermostat awhile back and now the furnace will not light. I checked the wiring and it's correct. The draft inducer motor will start and then shut off after about 5 secs. The furnace is a fairly new Rheem Criterion II FAU. The instructions for the thermostat say it can be used only with 24V or millivolt systems. I was thinking maybe my furnace is 120V. Can anyone help me in determining whether I have a 24V system or 120V system? The furnace troubleshooting guide says the igniter is 120V, but it doesn't mention anywhere what type of thermostat to use.
Thanks,
Brian

resercon
11-10-01, 01:08 PM
The electrical service to the furnace is 120V and a transformer drops it to 24V for your thermostat. There is a switch or a screw, usually in the back of these thermostats, that is used to make the thermostat either 24V or milivolt. The inducer fan will go off if the gas does not come on and the inducer fan would not have come on if the thermostat didn't call for heat. I suggest you call a qualified technician to come over and look at the unit.