In the season 3, episode 5 "Sight Unseen" Cole/Belthazor breaks into the Manor to prevent the demon Troxa from killing the Charmed Ones (Piper, Phoebe, & Prue) so he opens all the windows on the lower floor then turns up the AIR CONDITIONING to make it cold so the girls can see Troxa since he's invisible, but sensitive to cold. However, in the season 5 episode 22 "Oh my Goddess Part 1" Phoebe comes downstairs complaining about the heat and why they NEVER HAD air conditioning installed to which Piper explains it is due to the fact that they live in San Francisco where the temperature rarely gets above 75 (F).
The manor had air conditioning 3 years after the pilot yet they didn't have it 5 to almost 6 years after the pilot.
When Piper finds Chris reading their Book of Shadows, the page he's at shows a drawing in the likeness of Bela Lugosi. The two start talking, the pages are never turned, yet the next frame that the book is shown, the page has changed.