2005 Chevy Impala water pump

I recently changed the water pump on my impala as it was starting to leak, and filled the radiator and filled the reservoir halfway, and ever since I did this the temp guage has been rapidly fluctuating between 140 and 240, although never into the red zone. I have also noticed that since the change I have lost all heat, and only get very cold air now, where with the old pump I had the best heat ever, what could be the problem now?