Dec. 24 (Bloomberg) -- Jumbo mortgage shoppers in the most expensive U.S. housing markets such as New York and San Francisco aren’t getting much relief from lower borrowing costs.

The average 30-year fixed rate for home loans of more than $729,750 remains almost 2 percentage points above conforming rates and the spread between them may set a record this month, according to financial data firm BanxQuote.

Banks remain reluctant to lend after recording $678 billion in mortgage-related losses and writedowns in the past year and as house prices plunge. The collapse of the private mortgage securities market means lenders find there’s little demand for jumbo loans they want to sell. If low conventional rates entice enough homeowners to refinance, jumbo home loans may become more affordable as loan payoffs add liquidity to the banking system, said Keith Gumbinger, vice president of mortgage-research firm HSH Associates Inc. in Pompton Plains, New Jersey.

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