During an evening shift on January 13, an off-duty nurse reported that Mr Sigglekow had left work early feeling unwell, but he did not tell staff at the Puna Taunaki facility across the road and left a personal assistant on her own at the facility.
It was reported that by leaving the keys with the personal assistant instead of Puna Taunaki staff, he did not complete handover protocols.
It was also alleged that he had been sleeping on duty.
He responded to the allegation by saying he was "resting" and he considered resting in the workplace during a shift was an acceptable and normal practice.
But a WDHB clinical nurse director found Mr Sigglekow had breached the Nursing Council competencies for registered nurses because he had left an unregulated health worker in charge of patients with a history of high and complex needs.
A WDHB service manager considered a final written warning and a performance management plan but decided against it because it would not manage Mr Sigglekow's attitudes, which she considered were contrary to fundamental nursing practice.
Mr Sigglekow was sacked on April 21 despite receiving no warnings and having a previous clean record.
Employment Relations Authority member Rachel Larmer said the district health board's investigation was "so flawed" it did not have reasonable grounds for its conclusion of serious misconduct and dismissal.
Ms Larmer said matters of competencies for registered nurses were never raised with Mr Sigglekow and the dismissal letter he received did not refer to Nursing Council requirements.
The dismissal letter referred to a breach of district health board policy but he was never told what policy he had breached or why.
"I find a fair and reasonable employer could not have pursued disciplinary action against Mr Sigglekow before it had made it clear to him that behaviour which it had previously tolerated would in future be treated as serious misconduct, which may put his ongoing employment in jeopardy," she said.
Mr Sigglekow was awarded six weeks' pay but only $2000 of the $20,000 he sought for his humiliation, loss of dignity and injury to his feelings.
But Ms Larmer did not order the board to give Mr Sigglekow his job back.
She said reinstatement was not practicable or reasonable and was not appropriate given the level of his contribution to the situation.