I can't help you without more information. These cryptic statements are useless.
Make shure the wire to the temperature sending unit is installed properly.
What temp thermostat did you install? Use a infrared thermometer to see what temp the engine is running at. It will get warm even with no thermostat. Use a infrared thermometer to see what temp the heater hoses are after running it long enough to warm it up. After 30 min of fast idle is the top radiator hose warm/hot? is the thermostat housing hot /warm?
Is the system full of coolant?
I am still thinking it is the heater control valve.