BURNT OFFERINGS directed by Dan "Dark Shadows" Curtis in 1975.
This film has just been released on blu ray under its weird french title "Trauma"..:

I've watched this film on tv for the first time when i was a kid, in the late 80's...it gave me nightmares, especially the scenes with the "chauffeur" and the insane ending. 30 years later i"ve watched it on blu ray last week and i still think it's a creepy, pretty great movie!

Great performance from Olivier Reed and excellent supporting character performances from Karen Black, Bette Davis, Burgess Meredith, etc. Stephen King is a big fan of "Burnt offerings", both the film and both the Robert Marasco novel...it was an obvious influence on "The shining".
A well acted, well written, subtle, slow burn creepy movie, I would warmly recommend it as one of the best "haunted houses" movie, next to "The innocents", "Full Circle"/"The haunting of Julia" and "The entity". Also worth checking are others Dan Curtis tv works:
"Curse of the black widow", "Dracula" (with Jack Palance) and "Trilogy of terror" especially the story "Prey"/"Amelia" starring Karen Black.