I have a Trane 4 Ton Geothermal Single Stage Unit with a closed Horizontal Loop. The Thermostat is in the Great Room. I use a Propane Log in the Great Room fireplace as a backup heat source and didn't install the Resistive Heat Unit that normally backs up a Geothermal Heat Pump. The Propane Logs in the centrally located Great Room has a bimetallic switch to start a blower when the fireplace metal heats up to 115F to blow the heat into the room where a Ceiling Fan keeps the air in the room mixed & constant since a Cathedral Ceiling can hold the heat at the high point if no Ceiling Fan is used for air mixing. The Maintenance & Troubleshooting part of the post is having a Cold Room, which others have mentioned in the past due to thermostat location. I wanted the control of the Geothermal in the Great Room but needed control in a Remote Room. All air registers in the house have a damper at the main trunk to balance the air flow, but after a few years of making damper position changes I still can't compensate for the central location of the Thermostat as the outdoor temperature changes. Trying to keep a side room warm by setting the Thermostat in the Great Room higher caused the remote room to become too hot while the Great Room slowly heated up to setpoint temperature due to size of the Great Room. The Cure: I added a remote thermostat that only has temperature set point control, by running a thermostat wire from the Geothermal 24 vac to power the thermostat and one wire for Y1 to start and stop the Geothermal Unit. The room now stays at set point temperature, and if the Great Room temperature goes above set point the Remote thermostat keeps the compressor running until the Remote room temperature is met. The Gas Logs shut off due to a filled bulb temperature control keeping the Great Room from overheating. The extra run time on the Geothermal fan allows the Great Room heat to mix with the other rooms of the house. I could change out the Yellow Y1 wire for the Fan wire (Green wire) to start or keep the Geothermal fan running until the air equalizes the two room temperatures, but for now I'll take the additional run time on the Unit. This has solved our cold room problem. Since I couldn't find a schematic on line for adding a 2nd thermostat this was a Science Project for me which turned out as I suspected it would, but the unknowns such as potential overload & damage of the 24 vac Transformer in the Unit or the two thermostats working in parallel causing damage to thermostats were questions on my mind, and not having a spare 24 vac transformer on hand and needing to heat the house with the Geothermal Unit gave me some concern.