Home appliance firm Beko ignored a problem with its gas cookers for two months, an inquest has heard.
The cookers, make by Beko's Turkish parent company Arcelik, have been linked to 18 deaths in the UK and Ireland.
The inquest into the deaths of five people in two incidents in Cornwall heard Beko first found out about the issue in November 2008.
Beko said it had been waiting for formal test results from Arcelik.
Kevin Branton, 32, and Richard Smith, 30, died in 2010 in Saltash, while Audrey Cook, 86, John Cook, 90, and their daughter Maureen, 47, died in 2013 in Camborne.
Their cookers produced fatal levels of carbon monoxide when used with grill doors closed.
The inquest heard Mr Smith's cooker was bought on 31 December 2008.
Andrew Mullen, from Beko Plc, was asked what the company knew when and what actions it took in late 2008 and early 2009.
Mr Mullen said Beko was notified of the first fatality - that of French student Alexis Landry in Ireland - on 13 November.
Rob Harland, representing the families, said Arcelik provided Beko with a list of affected models on 2 December and said "a change had been made to all cooker models.... ending the problem in all new cooker production".
Mr Harland said by this point Beko knew the issue affected cookers sold in the UK and not just in Ireland.
Mr Mullen said Beko had not received the "formal" test results from Arcelik until 22 January.
Coroner Geraint Williams said: "There was a problem you should have acted on."
Mr Mullen said he accepted Beko had the information and "perhaps we should have acted differently".
Mr Harland asked why Beko waited for the formal testing report from Arcelik.
He said: "The presumption at this point is not that these products were safe, waiting isn't addressing the problem is it? It is simply ignoring it."
Mr Mullen said they waited for Arcelik to finish the testing.
The inquest continues.