I had to call honeywell tech support and they told me it is a return air temp sensor error, my system did not have one installed so tech support had me press and hold the connect button on the board until it started blinking orang, once i did that the thermostat reset the code and i was all good also if you have the thermostat to close it wont connect so when you go the connect the thermostat make sure you are about 10 ft away.