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."
