FRANKFURT (Reuters) - Shares in Siemens Healthineers SHLG.DE gained as much as 7 percent in the medical equipment maker's stock market debut on Friday, boding well for a string of pending German flotations including asset manager DWS.

In one of Germany's biggest listing in recent years, parent Siemens SIEGn.DE raised 4.2 billion euros from selling a 15 percent stake in the world's largest maker of medical imaging equipment.

Issued at 28 euros apiece, the shares opened at 29.10 euros after a delay of more than an hour because of market-wide technical problems at Deutsche Boerse's DB1Gn.DE electronic trading platform. By 1157 GMT the shares were up by 7.1 percent at 29.98 euros, outpacing a 0.3 percent gain for the benchmark DAX .GDAXI index.

Deutsche Boerse said it would take two to three days to investigate the technical problems but ruled out a hacking attack.

The offer price, which valued Healthineers’ equity at 28 billion euros, was seen by some market participants as a climbdown by Siemens to stoke interest in the issue.

Healthineers had been touted at between 26 billion euros and 31 billion euros, below initial expectations of up to 40 billion euros.

Investors have cited uncertain prospects for Healthineers’ flagship Atellica blood and urine diagnostics machines. It is also seen facing slightly more volatile markets, which have pulled valuations off record highs.

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Several large German listings are in the pipeline, with Deutsche Bank's DBKGn.DE asset-management arm DWS due to float next week. Publisher SpringerNature, property company Godewind, home-shopping group HSE24, fashion retailer Takko and online furniture retailer Home24 are all expected to follow suit.

EXTERNAL INVESTMENT

The Healthineers IPO, which investors have hailed as a pure-play medical technology investment, is among the biggest German listings since the start of the millennium. Deutsche Post DPWGn.DE and Infineon IFXGn.DE are top of the pile, both topping 6 billion euros when they listed in 2000, with Innogy's IGY.DE 2016 flotation raising 4.6 billion euros.

For parent Siemens, Healthineers’ market debut marks a key step in the group’s drive to attract external investors for businesses outside its core industrial engineering and automation operations.

It completed a merger of its wind power business with Gamesa SGREN.MC in April last year and agreed to create a joint venture with France's Alstom ALSO.PA for its rail operations.

Siemens wants Healthineers to be able to raise its own funds for takeovers and investments as well as crystallize its standalone value, removing some of the “conglomerate discount” that some investors say weighs on Siemens’ valuation.

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Healthineers’ management has promised growth from its Atellica platform by catching up quickly with established diagnostics competitors, but Sebastien Buch of fund manager Union Investment -- a top 10 Siemens shareholder, which is buying into the IPO -- voiced some doubts.

“A discount is warranted as investors are skeptical about how successful the rollout will be,” Buch told Reuters this week. “The preceding five Siemens diagnostics platforms continually lost market share over the last couple of years.”

Healthineers is on track to join Germany's mid-cap index .MDAXI in June via a fast-track entry mechanism ahead of the normal assessment date.

“With its expected free float market cap of about 4.2 billion euros, Healthineers currently ranks 18th and clearly exceeds the 1.9 billion needed for fast-entry inclusion,” said Silke Schluensen, index specialist at brokerage Oddo Seydler.

($1 = 0.8116 euros)