RHI inquiry will take over six months
Chairman Sir Patrick Coghlin said in a statement on the inquiry's website launched today, that the probe wouldn't be able to report in that timeframe.
The former High Court judge said it wouldn't be possible to give a completion date at this early stage of the investigation.
"The Inquiry will work as efficiently as it can, but we must carry out our investigation thoroughly and accurately. No one would thank us for producing a fast, but flawed, piece of work." He said.
"At present I can say that it will not be possible to report within 6 months, and I would draw attention to paragraph 17 of the Terms of Reference which simply provides that “The Inquiry will seek to work expeditiously and complete its report within a reasonable timeframe.” He added.
The inquiry was set up in January this year to investigate the botched renewable energy scheme, set to cost the taxpayer £490 million.
The debacle ultimately prompted the recent Northern Ireland assembly snap elections, after Sinn Fein's deputy first minister Martin McGuinness resigned and the Stormont institutions collapsed.
Arlene Foster established the scheme when she was DETI Minister in 2012.
Sinn Fein have maintained that they will not endorse Mrs Foster as first minister until the findings of the investigation are made public.
It's after allegations made by former Minister and DUP party colleague Jonathan Bell in 2016