Northumberland County Council has been left red-faced after staff failed to submit a planning application for a heating scheme.
Staff at the Stakeford depot installed a ground source heat pump but it has emerged they did not know they needed formal planning permission to do so.
But the blunder only came to light when the authority applied to claim its payments under the Renewable Heat Incentives (RHI) scheme and sought advice from the planning department, only to be told it should have applied.
At Tuesday's meeting of the council's strategic planning committee, Coun Ian Swithenbank said: "I know we have to treat retrospective applications like any other, but it hardly sets a good example to the rest of Northumberland."
The councillors were told that this was a slightly complicated situation as these installations are often covered by permitted development rights.
However, an application had to be submitted in this case as it lies outside the curtilage of the depot and the system contains more than one pump.
Planning officer Katherine Robbie said that this wasn't the only application of this type, with private businesses also being caught out by the rules.
Members voted to unanimously approve the bid, in line with the officer's recommendation.
