Hi, new member and first post, hoping someone can help with what I’m hoping is a small issue. I have a Rheem Classic 90 Plus Premium Efficiency gas furnace. I am replacing the OLD RobertShaw D3400 thermostats (original to the 1986 construction). I bought two Honeywell Non-Programmable RTH111B1024 thermostats. I hooked up one on the second floor, there were only three wires connected to the old thermostat - R, B, Y. I installed the new one and the temp was set to 67 degrees, but the heat kept running. I shut if off at 74 degrees. Is it a simple wiring issue? I figured I’d check here before contacting the Honeywell 800 number.
Thanks in advance….