* Fire damaged Boeing aircraft at London airport on Friday
* Investigators say no evidence of link to batteries
* Second Dreamliner suffers technical problems
* Airline "100 percent sure of its safety"
LONDON, July 14 (Reuters) - Airlines expressed confidence in the safety of Boeing's 787 Dreamliner on Sunday as investigators searched for the cause of a fire on one of the advanced jets and billions were wiped off the company's market value.
British officials said initial checks into what they called a serious incident appeared to rule out any link to the battery-related problems that grounded the Dreamliner fleet for three months earlier this year.
The fire on the Ethiopian Airlines plane at Heathrow Airport in London and a separate technical problem on a second 787 owned by Britain's Thomson Airways on Friday raised new questions about an aircraft seen as crucial to Boeing's future.
The incidents were a setback for a company trying to rebuild confidence in its flagship jet and compete with Airbus in the booming market for more fuel-efficient long-distance planes.
Britain's Tui Travel, which owns six European airlines including Thomson Airways, said its plane turned back during a flight from England to Florida and had a small number of unspecified components replaced. The parts were unrelated to the battery, it said.
"We want to reassure our customers that we have every confidence in this aircraft and would never operate it if we weren't 100 percent sure of its safety," a TUI Travel spokeswoman said.
No one was injured in the fire on the empty Ethiopian Airlines plane, which was parked at Heathrow. However, it closed Britain's busiest airport for 90 minutes.
Britain's Air Accident Investigations Branch (AAIB), part of the Department for Transport, said the damaged Ethiopian Airlines plane was being examined in a hangar at Heathrow.
Boeing shares closed down 4.7 percent at $101.87 on Friday after the Heathrow fire, knocking $3.8 billion off the company's market capitalisation.
In the early stages of the investigation, airlines said they would continue to fly their Dreamliners, while others confirmed they would stick to their plans to buy the aircraft.
Virgin Atlantic said it remained committed to taking delivery of 16 of the planes from the autumn of 2014. Delta Air Lines is buying a 49 percent stake in the airline.
"We are confident that Boeing and the relevant authorities are working hard to ensure that the appropriate action is being taken," Virgin said in a statement.
Polish flag carrier LOT, the first European airline to take delivery of the 787 last year, said it was in constant contact with Boeing.
Boeing will be keen to reassure airlines, travellers and investors over the cause of the fire as quickly as possible but under aviation rules it will be up to investigators to decide how much information to release and when.
Boeing said it had people on the ground working to understand the causes of the fire. The U.S. Federal Aviation Administration said it was in contact with Boeing.
Britain's AAIB said on Saturday there was extensive heat damage in the upper portion of the rear fuselage. The damage was far from the batteries and "there is no direct evidence of a direct causal relationship", it said.