ACT Sports Minister Yvette Berry revealed in an estimates hearing on Monday an agreement had been reached with the builder of the $27.8 million centre, which opened in 2014.

The 50-metre pool has been shut for the past 12 months, initially closed because of the coronavirus-induced lockdown before it was discovered in June some tiles were falling off.

The government admitted it still did not know what caused the tiles to fall off or what the total cost to the taxpayer would be, but Ms Berry expected the pool to be open by December.

Mystery has surrounded the pool's closure, frustrating swimmers and members of the Gungahlin community who have been unable to get answers.

Ms Berry said government agreed to the $400,000 payment from ADCO Constructions to avoid litigation, which would have prolonged the pool's closure.

"If we went through a process of litigation the pool would have been closed for a period of time," Ms Berry said.

The commercial settlement would allow the government to engage a contractor to remove and replace all the tiles in the problem pool. However, investigations undertaken by technical experts were not able to determine an exact cause into the problem tiles.

Major Projects Canberra chief projects officer Duncan Edghill was asked in estimates why the tiles fell off.

"It's a very good question and it's the question that's the obvious question we asked as well, unfortunately there is no clear answer as to what exactly caused the issues at the pool," he replied.

He said experts determined the tile problems could have been caused by a raft of issues, including problems with the adhesive used to attach the tiles, the movement of the tiles or the construction of the tiles.

When tiles began to fall off the pool was drained and technical investigations were undertaken into the cause of the problem tiles.

A report from the experts' investigations was delivered in December but repairs were unable to start until negotiations with ADCO Constructions had finished.

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ADCO Constructions has previously confirmed to The Canberra Times it was in discussions with the territory government about the pool. At the time, the construction firm would not provide detail citing privacy and legal reasons.

On Monday, a spokesman from ADCO confirmed the settlement but did not provide detail on the nature of the discussions with the territory government nor if the company had conducted its own investigations.

"We can confirm that the issues with the pool were technically very complex, but we can advise that a commercial agreement allowing the pool repairs to commence has now been reached," the spokesman said.

Liberal MLA Leanne Castley, a member in the Gungahlin-based seat of Yerrabi, said: "It is clear from minister Berry's remarks today we are no closer to finding out the truth about how much it will cost to fix the government's mess or how many more years Gungahlin residents will be without their pool."