Getting a issue in prius 2016

I have been using a toyota prius 2016 model for
One month everything is fine but now I encounter a problem and I don’t have idea what to do the problem is this
From last three days my car giving orange engine check light which only last for 15 mints in the morning when i start my car and then light disappear and whole day light will not shown but when i park my car in the night and start in the morning the engine check light come and after 20 to 25 mints light disappeared and nothing wrong with vehicle i got scanned it says water pump b circuit open the mechanic is saying change the water pump which cost me 400 pound but light only appear in first start in the morning then disappear even i ran my car 80 miles nothing wrong what should i do mow
From last three days same pattern in the morning first start light come after 20 mints light disappear and then whole day no light then in the next day in the morning light again came and again disappeared the error code is this
P261A13 water pump b circuit open