A senior civil servant has accepted his assumption that former minister Arlene Foster dropped cost controls from the RHI scheme was "incorrect".
John Mills made the claim in October 2015 as major changes were being made to tariffs.
Mr Mills was in charge of the energy division in the Department of Enterprise Trade and Investment (DETI), which ran the scheme.
His assertion was recorded in a departmental minute.
But, on Friday, he told the inquiry it had been an "assumption" on his part that there had to have been ministerial authority for the move.
He said in preparation for the public inquiry he had gone looking for documentation to back up the contention.
But he could find no evidence that Mrs Foster had taken any such decision.
The inquiry has been told that the introduction of the domestic scheme in 2014 had been prioritised over the need for cost controls.
Mr Mills said the decision appeared to have been taken in November 2013 just months before he joined the energy division.
He said the course had been set and he had simply followed it.
Earlier, he told the inquiry that his "perception" was that the RHI scheme had been "put in place to make sure that Treasury money was gotten hold of".
Money for the renewable scheme came from central government but conditions attached to the funding meant any overspend would affect Northern Ireland's block grant.
The inquiry has heard that was understood by officials in NI at the beginning but they lost sight of that fact as the scheme progressed.
When Mr Mills took over the running of the energy division, the non-domestic RHI scheme had been up and running for more than a year.
He said he was not aware of the need for a promised review and his focus was on the expansion of the scheme to domestic properties.
Mr Mills said persuading the then minister Arlene Foster of the need for cost controls, at a time when there was low uptake of the scheme and budget was being handed back to the Treasury, would have been a difficult sell.
He said even in the summer of 2015, when the pressure on the budget was clear, it still took several months to get urgent changes made.
By then, Democratic Unionist Party MLA Jonathan Bell had taken over as minister.