p0128 code

Problem with my Chrysler 2005 PT . The reservoiur water would bubble out at times. , no codes camed out on the dash board. The needle did not read overheat and it would stay right in the middle.
The fan did turned on and after few seconds it turned off. No codes came on nor the gauges would alert of an overheating. I figured it could be the Heat sensor. I replaced the sensor and the thermostat. Now I have a code reading p0128.? Correct me if I'm wrong; I installed one of those expensive thermostats that will prevent from closing up. I am thinking I need to replace it with a standard one or should I look further to solve the problem? like in the relays?