PORTLAND — Classes at Portland High School are canceled today because of a problem with the heating system.

An alert on the school’s website said there is no heat at the Cumberland Avenue school. Temperatures this morning were in the single digits.

Superintendent James Morse said the school’s backup boiler is out of service and the primary boiler was operating at about 25 percent. The problem became apparent at 6:45 a.m. and the decision to call off school was made at about 7:15 a.m., he said.

The students will not be required to make up the day as if it were a snow day because the entire school system was not called off, just one building, he said.