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The news is the latest in a series of disappointments for the problematic development, which had to postpone the opening of stage one for four months after issues with airtightness in its isolation rooms.
This time the issue is with ventilation systems for the isolation rooms in the new ward, which need to have their air changed 14 times an hour.
Southern District Health Board chief executive Chris Fleming said mechanical engineers contracted by the architects to deliver that system had been unable to do so.
"They have previously suggested changes to the air handling plant such as adjusting pulleys, increasing the size of the fan motors and adjusting the damper systems.
"However, nothing conclusive has come from their work to date and building and property have recommended ... that another party be commissioned to develop a design that will solve the issues."
Mr Fleming said managers had agreed to that recommendation, and a specialised report had been commissioned.
SDHB executive services director Patrick Ng did not expect a solution would be found quickly, and said the opening of the much-anticipated ward was likely to be months away.
"At this stage we anticipate that we may be delayed in our commissioning of the second stage of the ICU until the last quarter of the current calendar year," Mr Ng said.
"However, we will not have any real certainty until we have reviewed the report, quantified what changes need to be made and put these into a project timeline."
Stage one of the state-of-the-art redevelopment was welcomed enthusiastically by staff, but they now face a lengthy wait for what was intended to be a unified specialised critical care facility to be commissioned.
As with many construction issues in the clinical services building, its ageing facilities had caused problems for engineers, Mr Ng said.
"Unfortunately, the air handling systems in the current hospital are old, their current performance is not clearly specified and a programme to provide us sufficient certainty of what improvements need to be made (and how these will be achieved), needs to be developed."
Adding to the problems facing engineers was a decision by a previous board 20 years ago to detune the system as a cost-saving measure.