Whirlpool has admitted that there could be as many as 800,000 faulty tumble-dryers in homes around the UK.
In June, the government said it would issue a recall notice of up to 500,000 dryers which pose a fire safety risk.
But when pressed by MPs on the Business Committee, company executives admitted the number of unmodified machines could be higher.
A fault in Whirlpool machines was blamed for at least 750 fires over an 11-year period, the government said.
Whirlpool said it had logged 54 fires in its tumble dryers in recent years, three of which were in machines which had been modified.
Charlie Pugsley, deputy assistant commissioner at the London Fire Brigade, said his service had seen a wide range of faults causing fires in machines that had already been modified.
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Jemma Spurr was one customer whose modified dryer caught fire.
She told the Business Energy and Industrial Strategy Committee that despite repeated attempts to get in touch with Whirlpool directly, she had never received the report on the cause of her fire, or an apology from the company.
Whirlpool executive Jeff Noel apologised to Ms Spurr during the hearing and said the company had modified every machine bought to its attention.
Ms Spurr also claimed that Whirlpool asked her to sign a non-disclosure agreement (NDA) about the incident, which she refused to do.
Whirlpool said non-disclosure agreements were standard industry practice during insurance settlements.
By Colletta Smith, BBC consumer affairs correspondent
Faulty dryers, months to wait for a fix, continued problems even after modifications, and a full product recall. It’s a string of bad publicity for a company trying to brand itself as a provider of “quality home appliances”.
It wasn’t the first time that the company’s corporate vice-president had had to defend his products to a parliamentary committee. Jeff Noel previously responded to safety concerns about the company’s fridge-freezers which were blamed as the cause of the Grenfell fire.
Customers are understandably frustrated, and the white goods market is particularly dependent on trust.
Research by Deloitte suggests that people are more likely to read online reviews, and ask family and friends for recommendations of household appliances than any other purchase.
The string of damaging news has put Whirlpool is a real spin, as it comes at the same time as increased competition from the likes of Samsung, Bosch, Siemens and Zanussi.
Sue Davies, strategic policy adviser for Which?, told the committee about a review carried out by the Office for Production Safety and Standards.
She said it was “completely flawed” because it was based on “incredibly limited” data, much of which was provided by Whirlpool itself, and which she said contained gaps and inconsistencies.
Ms Davies added that it would be “absolutely incredible if Whirlpool are asking customers to sign NDAs” to obtain compensation.
Whirlpool also confirmed that during the recall period, customers can either have their current dryers modified or get a brand new machine free of charge, including installation.