(Reuters) — The brochure for Boeing Co.'s aircraft repair service makes a simple assertion: "No one knows Boeing airplanes better than Boeing."

Now that claim is being put to a visible test, as budget airline Norwegian Air Shuttle ASA grounded a brand-new, $212 million 787 Dreamliner over the weekend. The airline demanded Boeing fix the state-of-the-art jet, saying it needs repairs after less than 30 days in service.

Investment analysts say the glitch involving a hydraulic pump is minor and isolated, and it is unlikely to affect Boeing's stock price, which is towering at record levels.

But Norwegian Air's vocal airing of its complaints is another black eye for the troubled Dreamliner. It follows a string of electrical and other safety problems that included battery meltdowns so severe they prompted regulators to ban the long-haul jetliner from flight for more than three months this year.

On Sunday, Polish airline LOT 787 flying from Toronto to Warsaw was forced to land at Iceland's Keflavik airport after problems with its air system.

Norwegian Air's formal request on Saturday for Boeing to take charge of fixing the plane throws a spotlight on an often overlooked facet of the 787's performance: reliability. And it shows how quickly a plane that cannot fly can hit a carrier's bottom line.

Like other airlines with small long-haul fleets, Norwegian Air does not have a spare plane it can use if a jet breaks down. The carrier said it had to rent planes and cancel tickets when it could not use its 787s, and the company's stock has fallen 6% since a peak earlier this month, hit by a string of 787 problems and concerns about its broader business.

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"Reliability is a big deal, especially for low-cost carriers such as Norwegian," said Russell Solomon, an analyst at Moody's Investors Service Inc. in New York.

But since the problem appeared to be a "one-off" and part of the normal growing pains for a new plane, he added, it probably would not unsettle Boeing investors.

When Norwegian Air began long-haul operations this year, it aimed to capitalize on the Dreamliner's lower operating cost and the jet's promised 20% savings on fuel burn.

But the first two Dreamliners, delivered in recent weeks and part of a planned fleet of eight, broke down more than half a dozen times in September, forcing Norwegian Air to lease backup planes on short notice or cancel flights.

Norwegian Air grounded its 787s several times, citing problems with brakes, hydraulic pumps and power. On Sept. 23, the carrier said one Dreamliner was beset with problems in the oxygen supply to the cockpit. A problem with a valve on the airline's second 787 was repaired around the same time, but only after delaying a flight from Oslo to New York.

Boeing said the repairs of the latest problem, to be carried out in Stockholm where the aircraft is parked, would take a matter of days. That is much better than with the 787's volatile battery system, which grounded the worldwide fleet of Dreamliners from mid-January through late April.

"Boeing has identified a number of specific improvements to address component reliability," Boeing spokesman Marc Birtel said in a statement. The changes to hardware and software are "expected to lead to few schedule interruptions and significantly improve dispatch reliability."

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The plane's power panels, for example, which have suffered electrical arcing and other issues, have been improved already and will receive more upgrades in coming weeks, Mr. Birtel said.

Norwegian Air was the first to sign up for Boeing's GoldCare maintenance contract for its 787s, and is still the sole 787 customer for the plan. The brochure says GoldCare "significantly reduces the risk of new airplane introduction surprises" and helps airlines keep the plane in service.

But the grounded planes have prompted Norwegian Air to voice its dissatisfaction with the aircraft.

"The aircraft's reliability is simply not acceptable," Norwegian Air spokesman Lasse Sandaker-Nielsen said on Saturday.

"Our passengers cannot live with this kind of performance."

Saturday's announcement capped a tough week for Boeing in which Commercial Airplanes Chief Executive Ray Conner flew to Oslo to face Norwegian Air bosses over the earlier 787 mishaps.

Norwegian Air had laid blame on Boeing from day one, arguing that under its GoldCare service package Boeing was responsible for every fault and had an obligation to maintain reliability. Norwegian Air said it had asked the U.S. plane maker to face the press on Wednesday. But Conner didn't speak to reporters, despite mounting press criticism and comments from Norwegian Air that Boeing lacked adequate quality control.

"They didn't do themselves any favors at all when Ray Conner went to Norway and did not talk publicly," said Richard Aboulafia, an analyst at the Teal Group in Fairfax, Virginia.

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"There was no better signal for the airline to aggressively go public," he added.

Boeing promised to locate spare parts centers at all of the airline's long-haul destinations and send a team of engineers to the Nordics to monitor the planes.

Said Norwegian Air Chief Executive Bjorn Kos after the meeting: "It was a positive discussion."

On Saturday, however, when the jet needed further repairs, Norwegian renewed its criticism.

All new airplanes have teething problems when first entering service, and most are forgotten when the issues are ironed out. The Airbus A380 superjumbo had wing cracks that required reworking by the manufacturer, but that crisis faded from the headlines.

Boeing faces an additional test with the 787 and Norwegian Air because Boeing had claimed that the jet's advanced electrical systems and computerized fault-tracking would be both easier and cheaper to repair.

Boeing and rival Airbus also face a test of efforts to build lucrative after-sales service businesses to boost profit margins. Even as Boeing touts the reliability of its service, other airlines have been raising concerns about 787s.

A 787 operated by Poland's LOT airline had to land unexpectedly in Iceland on Sunday due to a fault in its air identification system, a spokeswoman for the airline said on Sunday.

Like Norwegian air, state-owned LOT airline has had a list of problems with its Dreamliners, including last week delaying flights after check-ups showed two planes lacked gas filters.

LOT also said last week that Boeing had until the end of the year to agree on compensation for the three-month grounding of the 787 because of the battery issues, or it would take the matter to court.

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Norwegian Air's GoldCare maintenance contract has served only to deepen Boeing's PR troubles by giving the company direct responsibility for sorting problem out.

Still, Solomon at Moody's said it would take significantly more than Norwegian Air and LOT's problems to dent investor confidence in Boeing as an investment, or a credit risk.

It would have to be "something that called into question the viability of the program," hurting Boeing's reputation and finances, he said.

Instead, Boeing is "performing quite well in these two important regards" and still has strong growth prospects for its commercial plane business.