The Ministry of Health is investigating stainless steel piping put into a Christchurch hospital building.
Contractor CPB has been issued a notice to fix the issue which might include replacing the hot water pipes in the $500m acute services building.
The new building - the country's biggest new hospital project - is overdue and over budget. Canterbury DHB's clinical leaders group has warned the ministry there are "major risks" for it due to building problems.
The ministry's engineering consultant Beca is investigating the plumbing.
"In the case of the pipes, the contractor has used pipes that were not approved by Beca," a ministry spokesperson said in a statement.
"This does not mean that they do not conform but just that they have not been approved. Moreover, Beca requires only one type of pipe system but have noted more than one.
"Accordingly, they are working with the contractor to determine what the final remedy may be."
That could involve replacement, but not necessarily.
"The non-conformity [notice] requires the contractor to remedy the issue which can be achieved in a number of ways including acceptance as is, replacement, or acceptance as an alternative solution. This is a normal practice and happens many times on a build and is used to ensure quality is maintained."
Warranties would not be voided and any extra costs or penalties would not fall on the ministry, but were a matter between the contractor CPB and plumbing subcontractor PHP.
Plumbing company Aquatherm supplies Mayer pipe and said it appeared PHP may have used it.
Aquatherm technical director Milton Sands said the product was fit for purpose.
"It has international testing and certificates. It also has Branz [appraisal] to prove that it meets the requirements of the New Zealand Building Code."
Commercial rivalries were behind questions being raised about the pipe's quality, he said, with a supplier spreading rumours.
Mr Sands said it was common to use more than one pipe system, and warranties remained valid as long as a mechanical joint separated the systems.
RNZ has been unable to contact plumbing subcontractor PHP.
Plumbing problems have proved costly at other hospitals. Wellington hospital is engaged in a long legal fight over myriad pinholes causing leaks in its copper pipes just a few years after installation.