Mrs O'Hagan says she's unhappy about how she was "portrayed" in the evidence given to the inquiry by two of the DETI officials she met.

She says that Mrs Hepper and Mr Hutchinson have claimed that her "main driver" was to "bad-mouth" to them that biomass boiler firms were trying to "put people off energy efficiency products" like hers.

"That was never, ever said... I didn't like that," she tells the inquiry, explaining that one such firm - BS Holdings - wanted to find a way to work with her to promote her product.

She describes their view as "inaccurate" and a "sweeping statement".

Mrs O'Hagan was advised by DETI to make her views about the RHI scheme known through the public consultation on the initiative.

When she looked at the consultation document and discovered it was primarily concerned with the new domestic RHI scheme she felt there was no place for her to make a response.

Image source, Getty Images

Mr Scoffield asks Mrs O'Hagan who did most of the talking at the meeting she had with DETI.

She says it was her and she presented her concerns "animatedly so and passionately".

Had DETI looked into her concerns about the RHI scheme it would've been "blatantly obvious" what the flaw was, says Mrs O'Hagan.

She says she doesn't know "how they could've missed the point" of what she was trying to tell them about the flaw in the RHI scheme.

Image source, Getty Images

"I question myself this a lot, and again and again I just don't understand."

She felt she "didn't really achieve anything" when she came out of the meeting.

Delving deeper into the events at the DETI meeting, Mrs O'Hagan says she had no sensation that the officials were pushing her for more information.

"I came away from that meeting thinking: 'They don't believe me; they don't take on board what I'm saying; I've been kind of dismissed'," she adds.

Image source, RHI Inquiry

Inquiry panel member Dr Keith MacLean asks if there was "a united front" among the DETI officials.

"Oh, definitely," says the witness.

Mrs O'Hagan told DETI that businesses she visited had the "heating kept on all year round with the windows open everywhere" due to the RHI scheme.

According to a record of the meeting that she put together in 2016 from emails from 2013, she also said that scheme claimants were "using more energy than before because it pays them to do so".

Image source, Getty

She also pointed out that there was "no incentive for them to be efficient".

She says she also told DETI that she was surprised some people weren't "mounting radiators on the outside" of their buildings in order to claim the scheme's overgenerous subsidy.

But those concerns were dismissed by the civil servants.

Image source, RHI Inquiry

Mrs O'Hagan told the DETI officials of the "potential abuse" of the RHI scheme but she says Mrs McCutcheon told her: 'We don't think people will do that.'

That statement will "stay with me to the day I die", says the witness.

DETI's energy team that was working directly on the RHI scheme met Mrs O'Hagan in October 2013.

She says she wanted to highlight DETI's error in making the scheme so lucrative.

Image source, Getty Images

Along with Mrs Hepper, the meeting was also attended by the two most hands-on civil servants dealing with the scheme, Peter Hutchinson and Joanne McCutcheon.

Mrs O'Hagan says it was an "important meeting for me" because "its not every day you get invited up there... and get an audience with the energy team".

Many people wouldn't know the correct procedures for complaining when grievances raised with public bodies aren't investigated, says Mrs O'Hagan, and a more effective route is to "go to the media".

Image source, DETI

"If somebody came to me in my business with concerns like that... I would certainty look into what that person was saying and I would do my due diligence."

She criticises the DETI officials, saying: "I didn't feel that was being done from them."

In reply to one of the initial emails, Mrs Foster sent a letter back to Mrs O'Hagan, saying that she couldn't meet due to a busy schedule, but she invited her to meet DETI energy boss Fiona Hepper and the team that was working directly on the RHI scheme.

There was no more contact between Mrs Foster and Mrs O'Hagan.

Image source, RHI Inquiry

Mr Scoffield notes that Mrs O'Hagan became increasingly frustrated in her dealings with the DETI officials, and he asks her why she didn't go back to the minister with her concerns.

She says she had other priorities - trying to build her business and see to her family - and she felt she had already brought the issue to the minister's attention.

"That's their job [to investigate it] - I can't really do any more", she adds.

Explaining the difference between the emails, Mrs O'Hagan says that because she was writing to the minister in the second one she wanted to "really add a bit more meat to the bones" and get her to "pay attention" to it.

But before receiving replies to the first two emails, she sent a third at the start of September 2013 - again directly to Mrs Foster and again requesting a meeting.

In that email she said that potential customers were not only losing interest in becoming energy efficient but RHI "pays them to use them as much as they can".

"In fact the incentive to use more is leading to misuse in some cases."

Crucially, that email was not forwarded by Mrs Foster to her officials at DETI, like she had done with the previous one she received.

The inquiry moves on to the key aspect of Mrs O'Hagan's involvement in the RHI scheme - her emails to DETI and Arlene Foster.

She says she got "fed up one day" and needed to say something so she sent the emails.

Image source, Getty Images

The first was sent to DETI's general information address in August 2013, and she asked for a meeting with the minister to discuss how her product could work alongside the "sustainability" of the RHI scheme.

On the same day, he also sent a broadly similar email to Mrs Foster's constituency address, again asking for a meeting.

She also explained to the minister that the benefits of the scheme meant "many of our potential customers are no longer interested in becoming more efficient".

Mrs O'Hagan contacted a boiler manufacturing and installation firm called BS Holdings to discuss the RHI scheme.

As the inquiry heard yesterday when its boss Brian Hood gave evidence, the firm produced promotional material marketing its products through the RHI scheme.

One of the slogans the company used was "20 years of free heat", and some of the material outlined how claimants could collect almost £1,500 from the scheme for every £1,000 they spent on fuel.

Image source, Getty Images

BS Holdings sent some of the material to Mrs O'Hagan and she says she wasn't shocked when she saw it because people were well aware of the scheme's benefits.

She tells the inquiry that BS Holdings was keen to discuss a potential business partnership but that "never really came to anything because what we did was at odds with what they were promoting".

Asked if she showed any of the promotional material to DETI when she met its officials, she said she didn't but there was "no appetite" from them for evidence to back up her claims.

There was a "bee in my bonnet" about how lucrative the RHI scheme that prompted her to email DETI and its minister Arlene Foster about her concerns, says Mrs O'Hagan.

She did her research on the similar heating initiative that was running in Great Britain, which had a crucial cost control in place called tariff tiering.

Image source, Getty Images

That works by dropping the subsidy rate on offer once a certain limit of heat usage has been reached, with the intention of preventing a claimant from overusing their heating system to collect more cash.

She says she knew the scheme needed that mechanism because without it people "were burning for profit".

Mrs O'Hagan sent an email to the then DETI minister Arlene Foster on 26 August 2013 after she had detected "a snowball of things happening" regarding RHI scheme.

Image source, RHI Inquiry

She had been noticing those things since the early part of 2013, and she tells the inquiry that something had emerged that "broke the camel's back", but she can't remember what that was.

"I would have talked to anybody about it and I did... right thorough from consultants to installers to general people within the energy industry," she says.

When she was promoting her product in 2013, Mrs O'Hagan went to trade fairs and noticed that her "target market" had a "distinct lack of interest" in saving energy if they were installing biomass boilers through the RHI scheme

She says their attitude was: "'What would I do that for? Sure I'm getting paid to heat.'"

That prompted her to look on DETI's website to check the subsidy the scheme was offering, and she "immediately" saw that it "can't be right".

She says she's "passionate" about energy efficiency and was "worried" about what she saw because it appeared to incentivise wasteful use of heat.

Mrs O'Hagan explains that she didn't consider herself to be a whistleblower because she understood that term to mean a person in an organisation who has "insider information about something that is done wrong within" it.

But in the case of the RHI scheme, she says the information was freely available to the public.

Image source, RHI Inquiry

She says that she went directly to the Department of Ehterprise, Trade and Investment (DETI), which was responsible for the scheme, rather than going to the media, like a typical whistleblower may have done.

"Because it was public knowledge it didn't feel [I was a whistleblower]."

Inquiry chair Sir Patrick Coghlin says the term is "meaningless" as far as he's concerned.

Mrs O'Hagan runs a County Antrim firm called Okotech, which specialises in developing energy-efficient heating controls.

Her product, called Heatboss, allows companies to wirelessly control heating in different rooms, the idea being to make commercial buildings more energy efficient and therefore reduce heating bills.

Image source, RHI Inquiry

She was trying to market her product shortly after the RHI scheme was introduced and became interested in the scheme because it appeared to disincentivise energy efficiency.

That was the basis of her contact with DETI between August 2013 and March 2015.

You can find Mrs O'Hagan's written witness statement on the inquiry's website, external.

BBC News Northern Ireland

On a lively day at the inquiry, a biomass boiler buinessman claimed that civil servants want to spread the blame for the disaster of the RHI scheme so that it doesn't all fall on them.

Image source, RHI Inquiry

Brian Hood's companies sold heating systems, and he rejected a Department for the Economy claim that there was a "conspiracy of silence" in his industry about the flaws in the scheme.

"They want to spread the net out and spread the blame to everybody as much as they can," he said.

BBC News Northern Ireland

An independent inquiry into the RHI scandal was established in January last year by the then finance minister Máirtín Ó Muilleoir.

He ordered it in the wake of the huge public concern and what was then a developing political crisis surrounding the scheme.

The RHI Inquiry began in November and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

Image source, Pacemaker

It will look at:

• the design and introduction of the RHI scheme
• the scheme's initial operation, administration, promotion and supervision
• the introduction of revised subsidies and a usage cap for new scheme claimants in 2015
• the scheme's closure

For more information on the RHI Inquiry, you can read our handy Q&A.

When the scale of the overspend emerged, public and political concern rocketed.

As the minister in charge of the Stormont department that set up the RHI scheme, the Democratic Unionist Party (DUP) leader Arlene Foster faced calls to resign from her role as Northern Ireland's first minister in December 2016.

Image source, PA

She resisted, and Sinn Féin's Martin McGuinness then quit as deputy first minister in protest at the DUP's handling of what had by then become a full-blown political crisis.

That move brought about the collapse of the Northern Ireland Executive. Now, more than a year on from that, Northern Ireland remains without a devolved administration.

You can find much more detail on the RHI scheme in our need-to-know guide.