The DUP has escalated a complaint against the BBC's Stephen Nolan show to media watchdog Ofcom.
The party took issue with a number of programmes in December 2016 covering the botched Renewable Heat Incentive green energy scheme and conflicting accounts of the actions taken by ministers, officials and special advisers.
Calling the BBC's response to the complaint "slow and utterly inefficient," the DUP has now taken the matter further to the regulator Ofcom.
In December 2016 the former DUP minister Jonathan Bell gave what was billed 'biased' as a "blockbuster interview" to Nolan detailing his concerns about how the RHI scheme had been mishandled.
In a tearful interview, Mr Bell said at the time: "I did not seek office to close hospitals while hundreds of millions of pounds are abused. I'll tell the truth and my political career will be ruined."
The DUP's Nigel Dodds complained to the BBC that the coverage surrounding the interview had been at times inaccurate, biased and unfair in its treatment of Arlene Foster who was First Minister at the time.
The BBC's Editorial Complaints Unit (ECU) said there were "no grounds" for complaints of bias or unfair treatment, but found the BBC's standards of due accuracy had been breached when parts of broadcasts on December 15 and 16 were repeated on December 27, 2016.
The programmes contained clips of interviews of both Mr Bell and Mrs Foster, framed with explanatory material.
Mr Dodds said Mr Bell had been allowed to make "baseless and demonstrably inaccurate" claims on air, noting that a senior official from the Department of Enterprise, Trade and Investment (Deti) had contradicted him.
The Deti official's statement had challenged parts of Mr Bell's version of events. As this wasn't released till December 18, ECU rules that the earlier broadcasts had not been inaccurate, but the December 27 programme should have included the Deti official's comments.
The finding has now been discussed with the Nolan show's senior editorial team, with a reminder that repeat broadcasts must be accompanied by any relevant updates about people and/or events featured within them.
A DUP spokesperson said: "The complaints were submitted by the party many months ago. The process has been slow and utterly inefficient. We welcome that a response has finally been forthcoming from the BBC.
"Whilst a complaint has been upheld against the BBC, the matter has now been escalated to Ofcom. We await the outcome of that process."
The RHI was designed to encourage businesses to convert to green energy by offering government grants. A lack of proper cost controls, however, meant that some applicants could effectively burn fuel to make money.
The political fallout brought the Stormont Assembly crashing down, with the crisis persisting to this day.
A public inquiry was set up last year to investigate the scheme's flaws.
Yesterday, the inquiry focused on a legal dispute on whether civil servants running the RHI scheme could be allowed to see the names and addresses of applicants.
Without this information, the concern was that officials could not tell if multiple boilers were being installed on a single site.