How RHI crisis caused a political firestorm
Here are the key events in the "cash for ash" scandal which looks set to lead to a snap Assembly election
June - Press Association reports allegations of a multimillion-pound "cash for ash" scandal in relation to the Renewable Heat Incentive (RHI) eco-scheme. In response, auditors confirm they are investigating.
July - An Audit Office report into RHI says "serious systematic failings" would hit the Northern Ireland budget by "hundreds of millions of pounds". The investigation was prompted when a whistleblower contacted the Northern Ireland Executive alleging that the scheme was being abused.
September - The Public Accounts Committee launches an investigation into the Audit Office's findings. A series of key officials involved in the scheme give evidence about an initiative one committee member brands "the biggest financial scandal since devolution".
December 14 - DUP MLA Jonathan Bell, who succeeded Mrs Foster as the minister of the department that set up the RHI scheme, breaks party ranks to level a series of allegations against the First Minister and party advisers in an explosive TV interview. He claims he tried to pull the shutters down sooner on the scheme but was dissuaded by Mrs Foster and DUP advisers. Mrs Foster disputes his account.
December 16 - Martin McGuinness calls on Arlene Foster to "stand aside" as First Minister while the "cash for ash" scandal is investigated. Mrs Foster replies that she will not be stepping aside and "does not take her instructions from Sinn Fein".
January 4 - Arlene Foster again insists she will not stand down over the RHI scandal, adding that some calls for her to do so are "misogynistic". DUP ministers say they are working on emergency legislation to bring the £490 million overspend to "zero". But Sinn Féin finance minister Mairtin O' Muilleoir says he is "bemused" that the DUP announced it to the media before talking to him.
January 5 - Former DUP MLA David McIlveen criticises Mrs Foster for what he describes as the RHI "omnishambles". Sinn Féin leader Gerry Adams says the political institutions have reached "a defining point" over the First Minister's refusal to step aside.
January 9 - Martin McGuinness resigns as Deputy First Minister in protest at the DUP's handling of the RHI scandal.
January 10 - Secretary of State James Brokenshire says the situation makes an assembly election look "highly likely". He calls for talks with all parties to find a resolution to the crisis at Stormont.
January 11 - Sinn Féin says it will not enter negotiations ahead of new assembly elections. British Prime Minister Theresa May says the government is putting "every effort" in to ensure a solution is reached.
January 13 - RHI inspectors say they have suspended payments at more than half the boilers they have audited. OFGEM said of the 63 inspected, payments were suspended at 33. Five have since had payments reinstated after investigations.
January 16 - Sinn Féin refuses to nominate a deputy first minister to replace Martin McGuinness, leaving Northern Ireland staring at a snap poll.