Peugeot 308 cooling fan

I had a bad alternator, replaced it and now the cooling fan is coming on full blast when it feels like, sometimes even when the engine is not up to running temp, switch off and restart engine, it stops for a while, but always runs slowly when you park up but for only a minute. I was going to try a new temp sensor but am a little bit suspect of it being something else as it only started happening with the alternator problem. Any help would be very welcome. Thanks, Paul.