Treasure Hill, the Westerly mansion owned by Karen and Louis A. Gencarelli Sr., features a sauna and heated pool.

GROTON, Conn. — A Connecticut couple has offered $4.5 million at auction for the Watch Hill mansion belonging to the owner of the defunct Bess Eaton coffee-shop chain.

The couple’s winning bid at the auction on Sunday is short of the mansion’s assessed value and could be rejected by Louis A. Gencarelli Sr. and his wife, Karen E. Gencarelli, who have been trying to sell the property — known as Treasure Hill — for more than three years.

The 17-room, 10,500-square-foot house at 2 Kidds Way on Watch Hill has an assessed value of close to $7 million, according to records from the Westerly tax office.

The Westerly-based Bess Eaton chain was sold in a 2004 bankruptcy court auction to Tim Hortons, the Canadian coffee-shop chain that was seeking to expand in the United States.

The Kidds Way house has been on the market since Louis Gencarelli pushed the coffee-shop chain founded by his family into bankruptcy.

The original asking price for Treasure Hill was $7.75 million. The house was built in 1988 to replace a house that burned to the ground in 1987.

Gencarelli bought the property in 2002 for $3.15 million from Anthony Fonda.

Treasure Hill stands on the second-highest elevation in Watch Hill and comes with a little more than one acre of land. It overlooks the Atlantic Ocean.

Amidst its layout, the mansion includes:

•a professional-grade kitchen with a six-burner Viking range/oven and Sub-Zero refrigerator

•seven bedrooms, eight full baths, and two half baths

•a three-stall attached garage

•a pub and game room

•a sunroom

•a fitness room

•a wine cellar

•a sauna

•a heated outdoor pool with a pool house

The Westerly estate was offered in an open auction, with New York-based Sheldon Good & Co. handling the event at the Mystic Marriott Hotel in Groton. About 15 people attended the auction, including at least two people relaying bids via cell phone.

Bidding yesterday opened at the $3 million suggested by the auctioneer and moved quickly above $4 million, but offers never threatened to approach the mansion’s assessed value during the auction’s roughly 15 minutes.

Mike and Diane McLean, of Simsbury, Conn., came out the winners at $4.5 million. A 7.5-percent buyer’s premium — $337,500 in this case — was added to the winning offer. A property closing will be scheduled within 45 days of the bid being accepted by the Gencarellis.

After the auction, the McLeans said they will use Treasure Hill as a vacation home. They plan only “cosmetic” changes.

In February of this year, Karen Gencarelli sold a house at 8 Cedar Rock Meadows in East Greenwich for $2.2 million, according to information from The Warren Group of Boston, a real-estate information service.

pgrimald@projo.com