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Acting principal Katrina Robertson said there were "electrical issues" which caused lights and plugs in some areas of the school to stop working.
But it was the loss of power to the boiler which prompted the school to close for the day, she said.
The boiler needed three sources of electricity to function, but only two sources were operating.
"The boiler was 100% affected and it meant heating was not possible.
"It was actually warmer outside than it was inside."
She believed the problem was caused by a faulty electrical conduit, which went from the transformer to the school.
"It’s suffered some damage. We’re not sure how or when it happened.
"It could have been when the dental hub was put in, it could have been as a result of the flooding — who knows?
"What has happened is, over time the conduit has slowly been corroding away and finally it’s got to the extent where it’s just given way."
Mrs Robertson said the school contacted the parents of its 180 pupils on Wednesday night when the problem was discovered, and told them not to come to school until 10am yesterday.
However, when it became clear the problem would not be resolved early yesterday, the school contacted parents again to say it was closed for the day.
A mixture of social media, texting, emailing and phone calls were used to contact parents.
She said a group of electricians, plumbers and power companies worked at the site yesterday and the school would be open today.