Volkswagen Repair: 2000 jetta, over heated once, thermostat switch, green fuse

Question
When stuck in downtown traffic the thermostat light came on and the needle was all the way buried to the right, I was one block from my destination so i continued, after sitting for an hour the car was fine and I went home. I know for a fact the fans did not come on, but my question is My machanic says he has to replace the waterpump ($750.00) i feel as though it is a thermostat switch that would turn on the fan to cool the engine, this happened once before 2o yrs ago on another jetta of mine. What do you thin? and thank you so much, Heidi  

Answer
There are a couple of heat sensors on your car. The fan switch sensor on the driver side bottom of the radiator and the sensor on the coolant flange driverside of the cylinder head. should be a black connecter or a green sensor. The best way to diagnose this is with the factory scantool. There are a few different cooling system fault the P0# would be helpful. The thermostats and water pumps come next. The thermostat sticks open allowing the warm up time to be longer.  The water pumps have the plastic impeller break on your engine causing no flow. The next problem would have to be the cooling fans. You say that the fans are not working. The fans have a 30Amp fuse on top of the battery. This fuse when looking at the battery cover is under the cover and inside the pocket. The fuse should be green in color and will be on the left of the three green fuses. Check the green fuse. A easy way to see if the fans are working is to turn on the ac and see if the fans spin. Your fans have two speed high and low depending on coolant temp and the ac pressure your fans will operate at different speeds. If the fans do not turn on when the ac is on then you have a problem. The fans both sides may be bad or the fan  switch or the fuse is blown which if it is then the fans are bad anyway. Replace the fuse if blown and retest. Wiring problem of the fan control module. The only way to be for sure is to see what temperature the dtc set in. -40degrees Celsius or 300degrees is two separate things. You do not have this capability so you have to check one thing at a time. So check the fuse. Turn on the ac and check the fans. Make sure the orange ac light is on and the blower motor is blowing out air then check the fans. Let me know how it goes. So the most like ly cause is the fans. Good luck.