The airport halted arrivals and departures at around 4.30pm on Monday (18 July) after a "surface defect" was identified.
"Flights are temporarily suspended to allow for an essential runway repair after high surface temperatures caused a small section to lift," the airport tweeted.
It came as temperatures across the UK reached 38C, with 40C forecast for Tuesday (19 July).
Luton issued a series of updates via Twitter, later confirming the runway reopened to departing flights at around 5.40pm.
At 6.15pm, it added: "The runway reopened to both arriving and departing flights at 6.05pm and is now fully operational."
Luton said it wanted to apologise for the inconvenience and thanked passengers for their patience.
