The wahealthplanfinder.org website went back online just after 2 p.m.
Michael Marchand, a spokesman for the new health insurance marketplace, says the problem was not related to the volume of visitors or to the federal government shutdown.
Marchand compared the experience to any new software launch and said glitches come with the territory.
Meanwhile, people continued to sign up for health insurance in Washington state by telephone or in person. Officials say it takes about an hour to go through the process for an individual or a little longer for a family sign-up.
Washington officials also warned people not to be fooled by fraud sites set up to look like wahealthplanfinder.org. Insurance Commissioner Mike Kreidler asked Washington residents to report any look-alike sites to his office.
Some of those sites were set up by licensed insurance agents, attempting to increase business, but others may be scammers attempting to get personal information such as Social Security numbers, said Richard Onizuka, CEO of the Washington Health Benefit Exchange.
Washington residents have six months to buy health insurance through the new exchange during the first enrollment period, which ends in March.
The state estimates about a million Washington residents do not have health insurance, or about 1 in 7 people.
The state hopes to enroll 130,000 people for health insurance in 2014 and another 280,000 in 2015.
Another 325,000 people will be eligible to sign up for free insurance through Medicaid.
Under the Affordable Care Act, people who don't have insurance in 2014 will pay a fine when they file their federal income taxes in early 2015. The fines for people who ignore the new law are scheduled to increase over time.
"We want 6.5 million people to go to healthplanfinder to check it out," Marchand said Monday.
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