An urgent appeal has been issued over certain models of gas cookers that, in some circumstances, can cause carbon monoxide poisoning.
Derry City Council issued the warning on Thursday but it applies to all areas of Northern Ireland.
BEKO, Leisure and Flavel cookers with a separate oven and grill are affected.
Some customers have still not been identified despite a previous appeal and efforts by the manufacturers to contact them.
A spokesperson for Derry council's environmental health department said: "We are concerned about this issue and would like to encourage anyone who has bought these cookers to get in touch with the manufacturer.
"Given the serious risk of carbon monoxide poisoning if the grill is used while the door is closed, we are urgently calling on consumers to check their cookers today."
The council urged all consumers with gas cookers - including landlords and letting agents - to check if their cooker is one of the models affected.
If so, they should contact the manufacturer helpline number to arrange for it to be modified free of charge.
The spokesperson added: "Under no circumstances should anyone operate the grill with the grill door closed - it must always be in the open position.
"It is also essential that people do not use the cookers as heaters or for any other purpose than cooking."