I have the Honeywell RTH230B Thermostat. I do not have A/C. I have a gas heated, gravity system. My problem is that I have 3 wires coming out of the wall. Im confused. I am used to themostats having 2 wires. Can anyone help?

What are you trying to do? Ye olde 2 wire thermostats connected a hot wire from the transformer to one side of the gas valve. The Honeywell RTH230B Thermostat will do the same. It will have an RH terminal, connect the hot wire, usually red from the transformer to it. Connect the wire to the gas valve, often white to W or W1. The Honeywell RTH230B Thermostat may require a third wire from the other side of the transformer connected to the B or C terminal. Otherwise, it is not used in your system. If you do not have red and white wires, the wires you do have may be connected to terminals marked R and W at the furnace. Even if you have red and white wires, you might verify where they are connected at the furnace.

I notice some new members here. I hope they know more about the Honeywell RTH230B Thermostat than I do. If so, I may leave these questions to them. I have more to do than get in the way of people that can give better answers than me.

What are you trying to do? Ye olde 2 wire thermostats connected a hot wire from the transformer to one side of the gas valve. The Honeywell RTH230B Thermostat will do the same. It will have an RH terminal, connect the hot wire, usually red from the transformer to it. Connect the wire to the gas valve, often white to W or W1. The Honeywell RTH230B Thermostat may require a third wire from the other side of the transformer connected to the B or C terminal. Otherwise, it is not used in your system. If you do not have red and white wires, the wires you do have may be connected to terminals marked R and W at the furnace. Even if you have red and white wires, you might verify where they are connected at the furnace.

I notice some new members here. I hope they know more about the Honeywell RTH230B Thermostat than I do. If so, I may leave these questions to them. I have more to do than get in the way of people that can give better answers than me.

But I have 3 wires coming from the wall. After I connect the power supply an the heating signal wire where does the 3rd wire go?

''The Honeywell RTH230B Thermostat may require a third wire from the other side of the transformer connected to the B or C terminal. Otherwise, it is not used in your system.''

If you don't have A/C or a blower for the furnace, it doesn't need the third wire. If the thermostat doesn't need a third wire, leave it unconnected.

I have the Honeywell RTH230B Thermostat. I do not have A/C. I have a gas heated, gravity system. My problem is that I have 3 wires coming out of the wall. Im confused. I am used to themostats haveing 2 wires. Can anyone help?
I'm not sure of the 3rd wire either. You need to find out where each of these 3 wires go on the furnace. Old gravity furnace means there is not a blower motor, thusly the air moves by the rise and fall of hot and cold air. Many of the old gravity furnaces also have no transformer, instead they use a powerpile to supply the voltage and a millivolt thermostat "must" be used.

''The Honeywell RTH230B Thermostat may require a third wire from the other side of the transformer connected to the B or C terminal. Otherwise, it is not used in your system.''

If you don't have A/C or a blower for the furnace, it doesn't need the third wire. If the thermostat doesn't need a third wire, leave it unconnected.

I did leave the 3rd wire unconnected an the stat works perfectly thank you guy

The answer was just what I was looking for, Thanks