Democratic Unionist leader Arlene Foster is facing increasing calls to stand down pending an independent probe into an error-ridden scheme that has landed the Northern Ireland taxpayer an estimated bill of £400 million.
Alliance Party leader Naomi Long joined all other parties in the Assembly except the DUP in a mass walk out during a speech by the first minister.
Foster denounced opposition parties as "irrelevant and impotent" as she responded to an Assembly motion of no confidence in her.
But Long told Premier's News Hour her actions were "a direct threat to the devolved institutions and the structures of government".
Foster's decision to break parliamentary rules and give a speech that was not approved by power sharing partner Martin McGuiness was "fatally flawed", Long added.
She said: "I think it is hugely important that she listens to the anger in the public domain, that she listens to the concerns of the people of Northern Ireland who are genuinely annoyed at the amount of money that has been wasted because of the mishandling of this situation."
Alliance Party leader Naomi Long
Foster's Renewable Heat Incentive (RHI) was due to offer a proportion of the cost businesses had to pay to run eco-friendly boilers, but it ended up paying significantly more than the cost of fuel, enabling applicants to "burn to earn" - getting free heat and making a profit as they did it.
Claims of widespread abuse include a farmer allegedly set to pocket around £1 million in the next 20 years for heating an empty shed. Mrs Foster was the minister in charge of the scheme at its inception.
The DUP leader said she would not run away from her responsibilities.
"I remain as committed today as I did on the day I was elected as First Minister to fight the good fight, finish the race and keep the faith."
Naomi Long speaking to Premier's Antony Bushfield:
