Thai Airways and Turkish Airlines will not move into Heathrow's new Terminal 2 on Wednesday as scheduled due to "unplanned testing" of baggage systems.
Both Star Alliance airlines will now begin operating out of the terminal later in the summer, the airport said. Eva Air and Avianca, however, will still be moving into T2 this week.
The postponement is due to problems with the Terminal 5 baggage system that has resulted in some luggage being processed manually, causing disruption. Heathrow has extended testing of its baggage handling systems to T2.
Thai Airways said in a statement: "As Heathrow airport will conduct unplanned testing of its baggage systems, Thai's planned move from Terminal 3 to Zone A of Terminal 2 has been postponed from July 2 until later in the summer.
"Until the new move date, flights will depart as normal from Heathrow Terminal 3. Thai's postponed move will allow Terminal 2's baggage systems to be further trialled and tested to ensure that it works properly."
A statement from Heathrow added: "We have been experiencing intermittent issues with the Terminal 5 baggage system which has caused some bags to be processed manually.
"While passengers can currently check-in bags as normal, you may wish to carry essential items in hand baggage where possible. Flights are still operating as normal. Our engineers are closely monitoring the system.
"Manual processing led to some bags not making flights in time. Passengers are receiving bags all the time but it will take several days to reunite all passengers with their bags."
Last week, the Queen officially opened Terminal 2, some 59 years after she opened the original terminal (see news, June 23).