Dustin Diamond[1] needs to be saved by more than the bell if he wants to keep his home in Wisconsin -- the bank is knocking on his door and looking to foreclose.

The "Saved By The Bell" star owes Wells Fargo a whopping $269,329.36 -- according to legal docs obtained by TMZ -- and the bank is asking the court to sign off on the foreclosure.

Dustin tells TMZ ... he didn't even know he was so far behind on the mortgage, because he hasn't been to the Port Washington property since January of last year, as he's been living in Florida instead.

Screech says he moved into the house way back in 2003, when the property was worth $340,000, and tells us he plunked down a $68,000 down payment. He says he doesn't understand how he owes such a large sum. Homeownership ain't easy, or cheap.

Dustin's got a lot of other problems at the pad ... he says a friend alerted him to a busted water main last fall, and the leak was so bad water was flowing out of a first-floor window.

Screech says he lost 30 years of memories in the home's flooded basement ... his comic collection, instruments, chess collection, family pictures and videos were all ruined.

Dustin tells us ... "Foreclosure means nothing when a house is destroyed ... with my items I've lost, it now feels like Wells Fargo is trying to kick me when I'm down."

He says he never went to check on the pad last winter because his friend said the water main break froze over, and there was black mold. He was waiting for the ice to melt to return, but the pandemic ruined that plan.

Dustin still hasn't been back there, and says he

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