OK, just bought a Honeywell RTH2300 to replace an older thermostat in my house. Only 2 wire, so single stage gas/steam furnace. 2 wires coming in, green and red, which I hooked to green and red on thermostat. Well, furnace only fires when I switch the fan switch from auto to on. Near the breaker, the wires are labeled coming out: gas burner with the green wire and thermostat with the red wire.

Help!

Red to r
Green to w