Kewaigue Hill (Castletown Road) will be closed from 9:30am on Friday July 10 until the evening of Sunday July 12 to allow remedial works on the newly installed pipeline.
The closure comes after a defect was identified during the final inspection and testing of the pipeline at Kewaigue Hill.
All new Manx Utilities infrastructure undergoes a rigorous inspection and testing process before it is accepted from the contractor and brought into service.
As part of this process, a CCTV survey identified the issue, which must now be rectified before the asset can be accepted and final handover can take place.
The road will reopen earlier if the work is completed ahead of schedule.
A Manx Utilities spokesperson said: “We appreciate that this additional closure will be frustrating for residents, businesses and road users. However, completing these works now will ensure the defect is resolved before the pipeline is brought into service and will help avoid the risk of more significant disruption and costs in the future.”
The spokesperson added: “We apologise for the inconvenience and thank everyone for their patience and understanding while this final stage of the project is completed.”