BBC News Northern Ireland

An independent inquiry into the RHI scandal was established in January 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.

Image source, Pacemaker

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

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 last year.

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, and as we near a year on from that Northern Ireland remains without a devolved administration.

If you want a bit more detail on the background to the scandal and the subsequent inquiry, here's our need-to-know guide on the RHI scheme.

There were critical flaws in the way the RHI scheme was set up that left it open to abuse and that later saw its budget spiral out of control.

Crucial cost curbs that existed in a similar scheme in Great Britain were not replicated and claimants could effectively earn more money the more fuel they burned.

Image source, Getty Images

That was because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves - the scheme was later nicknamed "cash-for-ash" for that very reason.

As a result, the scheme racked up a huge projected overspend - £700m at the most recent estimate, if permanent cost controls are not introduced - and the bill will have to be picked up by the Northern Ireland taxpayer.

Need a quick refresher on the Renewable Heat Incentive (RHI) scheme? Well, we're here to help...

It came to the fore of the Northern Ireland public's knowledge in autumn last year - few people, if anyone, would have expected it to have the consequences it has done in the months that followed.

It was set up by the Northern Ireland Executive in 2012, as a way of encouraging businesses to switch from using fossil fuels to renewable sources for generating their heat.

Those who signed up were offered financial incentives to buy new heating systems and the fuel to run them.

After a bizarre day yesterday in which Stormont was, for a while at least, at the heart of the Brexit action, things have settled down a little bit at Parliament Buildings... for now at least.

In the meantime, the RHI Inquiry resumes, entering its fourth week.

Image source, Pacemaker

Facing a full day of questioning will be Peter Hutchinson, one of the civil servants who was involved in the Renewable Heat Incentive scheme at its outset.

We have live video coverage and text commentary to keep you updatefd throughout the day.