What could cause a heat pumps line sets to be the same temperature when running?
If the lines are the same temperature, that means they're at the same pressure.  Which is normal when the system is not running.  Once the system starts, the pressure in one line should go up, while the other goes down. 

Since the pressures in your system are basically equal, I'd say the refrigerant is low.  You can verify this be connecting a set of gages to the system, or having a local HVAC technician do it for you.  If the refrigerant is low, it's likely you have a leak. The HVAC technician should be able to find and repair the leak, and recharge the system.