When you start to shop around for HVAC systems and thermostats, you’ll find an incredible variety of brands, models, and configurations.
If you have recently invested in a new HVAC system or smart thermostat, chances are that the devices are not compatible. Unless you intend to change the entire system, you may want to check if the new appliances will work with the old ones before purchasing.
As explained above, the thermostat draws power from the HVAC system. If the two devices are not compatible, that could be the reason why there’s no power to thermostat wires.