My old thermostat was a Hunter MOdel # 44260 with wires connected to the G, RH, Y/O, & W/B connectors. There was a Jumper wire connecting from the RH to the RC. It's a 24 volt Honeywell system in the attic which controls both the heat & A/c. My heat is natural gas, while my A/C is regular with an outdoor compressor. NO heat pump. When I first installed the Nest, it told me I might need a C Wire/Power Connector. I was getting an E294 error at that time. Then after a couple resets, I started getting a message saying in couldn't fine the G wire, which made no sense and giving me an E257 error code. I connected the wires properly and am getting pissed at this - ready to return it... I have installed Dishwashers, Water Heaters, refrigerators, Washers & Dryers, ran dedicated electrical wiring circuits to my breaker box. This is a pain in the butt. Need help or both of the Nest units I bought will get returned... 
