The National Capital Authority chief operating officer Lachlan Wood said while staff and contractors had been working hard to limit the fountain's downtime, manual operation had now become impractical.

To try to limit delays the authority has brought forward its maintenance program to coincide with repairs.

Completing the required repairs and maintenance works to the jet whilst not operating will create efficiencies and minimise the jets overall down-time," he said.

"Phase one of the project will see the refurbishment of the flow control valve located within the pump-station replaced, with parts due to arrive from England within the coming weeks."

After the completion of phase one, it is expected that the jet will operate intermittently to allow for the testing and commissioning of the refurbished control valve.

Phase two of the project will see scheduled maintenance completed on the jet including the fitting of a new access system to the jets outlet structure, ensuring safe access to the jet.

The jet is expected to be operational by mid-2019, when it will return to being run from 11am to 2pm daily.

The jet was inaugurated by Queen Elizabeth II on April 25, 1970, almost 50 years ago.

More than six tonnes of water is pumped into the air, leaving the jet at about 260 kilometres an hour.

The jet is a complex piece of infrastructure, which requires ongoing repairs and maintenance to ensure it remains as one of Canberras landmark attractions, Mr Wood said.