Children had to be collected by their parents and carers after a rogue radiator cut the school day short.
After a long summer of not being utilised, a radiator was turned on today at Belmont School, in Hibbert Road, Harrow Weald, to battle the Autumn chill.
However it soon burst, with flooding so severe that Year One students on the floor below were sent home after the water had come into their class.
A Harrow Council spokesman confirmed that the problem has been addressed, and that dehumidifiers have been drafted in to ensure that children can return to school tomorrow unaffected by the leak.
He added: "One of the carpets got quite wet."
The headteacher informed parents of the issue via text messages.
The reception class at the school had their start to the term delayed after an asbestos discovery by builders over the summer.
