Stafford School has been shut since Monday after both boilers which serve the school failed, leaving it without heating at a time when temperatures have been dropping below freezing.
The school's headteacher, John Sargent, called the situation 'most regrettable' and said as the problem was discovered over the Christmas period, suppliers were not available to rectify it before the start of the new term.
But one parent claimed the school had known of problems with the heating since early December, when a sign on the school gates recommended children wear extra layers of clothing.
Pupils should have returned after the Christmas break on Monday but the boiler problems meant the school stayed closed.
A notice was posted on the school's gates on Tuesday. It read, "Stafford will be closed on Wednesday 7, Thursday 8 and Friday 9 January because of lack of heating."
A further message, on the school's main telephone line, said, "Stafford Junior School is closed from Tuesday January 6 to Friday January 9 due to faulty central heating.
"Updates on the situation will be announced on local radio and the school gates."
A disgruntled mother said, "It's not on the website - I got a text from a friend who had heard it on the local radio.
"A lot of people were caught out and turned up at the school on Monday. There was a notice on the gate saying it wouldn't be open Monday and Tuesday because of heating problems.
"There has been no apology and they have known about this since the beginning of December.
"It's difficult when you work. I have had to rely on relatives and try and take time off work. It's a problem after the long Christmas break when I have been at home with them."
Mr Sargeant said he had 'every sympathy' with working parents who had
been inconvenienced.
He told the Herald, "This has been a most regrettable, but completely unavoidable, situation.
"I can fully understand the anxiety of parents whose children are missing valuable learning opportunities.
"I can understand their frustrations at being inconvenienced regarding their personal or work situations.
"They have my every sympathy and I am grateful to them for their patience and understanding.
"The simple fact is that, at the very worst time of year in the severest weather conditions, both boilers that serve the building burst.
"Because of the Christmas and New Year period, it has been impossible to source the required parts and then get the extensive repairs made in time for the new term.
"In these circumstances, the buildings have been extremely cold – the best temperature achieved has been six degrees and this is far below the required temperature for children and staff to work and learn.
"The staff have been wonderful and have tried hard to keep preparing for the new term in these very poor conditions.
"We hope that as soon as the problem has been solved we can make a flying start to the new term."
East Sussex County Council said it was doing 'all it can' to rectify the situation.
A spokesperson said on Wednesday, "Work has commenced on site to replace cracked sections to both boilers.
"It is anticipated that this work will be completed by the end of the week.
"It was unfortunate that problems only became apparent over the Christmas break as this meant suppliers for the specialist replacement parts were closed for the festive period.
"It is also an extremely unfortunate coincidence that the fault occurred to both boilers thus disabling the backup facility provided by the second boiler that would have kept the school operational."