RX400HBmore

My RX400h 2006 Lexus was overheating and the dash had the warning water temperature. I took it to a Lexus Dealer and they told me that my radiator had a leak, so they replaced my the hybrid radiator which is located in the front of the vehicle. They then called me to tell me that the radiator was installed, but it did not stop the car from overheating. They then said it maybe the thermostat and if that doesn't fix the problem then it could be the water pump or the head gasket. I also asked them for a copy of the diagnostic which they originally told me it was on the computer. I then t old them to print me a copy. The Diagnostic showed there was a code P0A1B. I asked the service technician what does that code mean and he indicated it was the code for the hybrid radiator. I had the car seen by another mechanic and they told me that the P0A1B code means the inverter is going up. He also indicated that the Lexus dealer should not have repaired the inverter radiator because nothing was wrong with it when he looked at the car. He is now asking me to replace the thermostat, timing belt and water pump. I don't want to put more money into the vehicle if this isn't going to stop the car from overheating. Please help me to make a decision on what to do or what maybe the real problem.