Pupils at a German school were allowed to strip down to beachwear after the heating system stuck on full power.
The piping hot radiators left classrooms sweltering in 30 degrees centigrade, even with all of the windows open.
So staff announced children could wear swimwear – including bikinis and swimming shorts – in class until the radiators could be fixed.
The Anne Frank primary school, in Linden, only recently had the expensive digital heating system installed and experts have been unable to identify the problem.
School headmaster Bruno Kraft said: “We have been having problems ever since they installed the new, fully digitalised heating control system.”