Arlene Foster has said she did not sign a blank cheque for the Renewable Heat Incentive (RHI) scheme.
Northern Ireland's former enterprise minister said officials should have given her more information.
Mrs Foster gave evidence to a public inquiry established to investigate flaws in the botched Stormont green energy initiative, which ultimately led to the collapse of the powersharing Government.
She said: "I read the information given to me, I took the information at face value."
With hindsight she believed she should have received more information, adding: "I don't believe it was a blank cheque at that time."
The DUP leader said she did not read some technical information associated with the scheme but it was up to others to flag up issues raised by that in their submissions to her.
She said she did not know why that was not done.
A panel chaired by Sir Patrick Coghlin is investigating the RHI scheme.
Panel member Keith MacLean has previously suggested it was given a blank cheque.
On Wednesday, Mrs Foster said she was not aware of the final bill when the scheme was in its formative stages.
She was enterprise minister when it began in 2012.
A series of fatal design flaws exposed Stormont to a huge overspend, paying out more than it cost to buy wood fuel.
This created an incentive to "burn to earn".