By Donna Cassata and Martin CrutsingerWASHINGTON -- The United States moved closer to the possibility of the first-ever default on the government's debt Sunday as Speaker John Boehner adamantly ruled out a House vote on a straightforward bill to raise the borrowing authority without concessions from President Barack Obama. With no resolution in sight, Treasury Secretary Jack Lew warned that Congress is "playing with fire" as he called on lawmakers to quickly pass legislation re-opening the government and a measure increasing the nation's $16.7 trillion debt limit. The government shutdown precipitated by the budget brinkmanship entered its sixth day with hundreds of thousands of federal employees furloughed, national parks closed and an array of government services on hold. Lew said Obama has not changed his opposition to coupling a bill to re-open the government and raise the borrowing authority with Republican demands for changes in the three-year-old health care law and spending cuts. Boehner insisted that Obama must negotiate if the president wants to end the shutdown and avert a default that could trigger a financial crisis and recession that would echo the events of 2008 or worse. The 2008 financial crisis pushed the country into the worst recession since the Great Depression of the 1930s. "We're not going to pass a clean debt limit increase," the Ohio Republican said in a television interview. "I told the president, there's no way we're going to pass one. The votes are not in the House to pass a clean debt limit, and the president is risking default by not having a conversation with us." Boehner also said he lacked the votes "to pass a clean CR," or continuing resolution, a reference to the temporary spending bill without conditions that would keep the government operating. Democrats argue that their 200 members in the House plus close to two dozen pragmatic Republicans would back a so-called clean bill if Boehner just allowed a vote, but he remains hamstrung by his tea party-strong GOP caucus. "Let me issue him a friendly challenge," Sen. Chuck Schumer (D-N.Y.) said. "Put it on the floor Monday or Tuesday. I would bet there are the votes to pass it."