A similar incident occurred on Saturday with a ventilator that was produced in the same factory.
Russian authorities said they would look into the safety of artificial lung ventilators being used at two hospitals after a fire broke out in St Petersburg at one of them on Tuesday morning and killed five people.
The blaze erupted after a ventilator in an intensive care ward treating 20 patients with the novel coronavirus burst into flames, one source told the TASS news agency.
It was the second fire to break out at a hospital treating coronavirus patients in less than a week. A similar fire erupted at a Moscow hospital on Saturday, killing one person.
A TASS law enforcement source said that a ventilator had caused that fire too. The source said the ventilators that caused both fires had been produced in the same factory in the Urals region.
Roszdravnadzor, Russia's federal service for supervising healthcare, said it would check the quality and safety of the ventilators in the two hospitals, the RIA news agency reported.
Investigators opened a criminal case into Tuesday's fire.
A hospital in St Petersburg will stop using the Aventa-M model of lung ventilators until the investigation is complete, Russian media reported.
Russia is relatively well stocked with ventilators and has increased domestic production since the coronavirus outbreak. But data, experts, and some medics say many machines outside big cities are old.
In this case, however, the ventilator reported to have started the St Petersburg fire was new, TASS reported, having only been installed this month.
A third fire broke out on Monday at a private hospice in the Moscow region which killed nine elderly people outright.
The hospice's owner was detained by police. A further two people later died in hospital, the RIA news agency reported.
Russia has reported 232,243 cases of the novel coronavirus, the second highest number of cases in the world as of Tuesday morning, according to the Johns Hopkins University in the US, and 2,116 deaths.