The Premier Colin Barnett has refused to concede that an extra $100 million spent on bringing the Muja power plant near Collie on-line is a blowout.

The 46-year-old plant had been mothballed but after the 2008 Varanus Island gas explosion the State Government committed $150 million to bring it back online and guarantee the State's power supplies.

But pre-election financial projections released yesterday revealed there has been a $100 million cost blowout and further delays to the plant's full re-opening.

Opposition Energy spokesman Bill Johnston says Mr Collier must be held responsible.

"Mr Collier should resign today," he said.

"It is unbelievable that there would a $100 million blowout in a $150 million project. There must be accountability in this. Mr Collier must be held responsible."

The Energy Minister Peter Collier admits there has been a cost blowout in bringing Muja back on-line saying it is due to technical problems.

"Now these issues have risen from highly technical and complex boiler issues, the likes of which have not been seen in Western Australia before," he said.

"The safety and the current future workforce is of paramount importance to the West Australian Government.

"We are confident as a government that the Muja A-B project will be profitable for Verve Energy in the future."

Mr Barnett says the extra cost was due to the boiler requiring extensive work but he refuses to concede the extra $100 million is a blowout.

"We are not going to compromise on the efficiency of the operation of the power station or the safety of the people working in it," he said.

"A blowout is when you set out an area of work and you find it costs more. What we have found is more work will need to be done on that power station than originally anticipated."