Millions of owners of potentially lethal tumble dryers have been warned not to use them, while they await repair.
Tumble dryers sold under the Hotpoint, Creda and Indesit brands have been behind a series of fires.
Their owner Whirlpool had previously said they were all right to use, providing someone was in attendance.
But following advice from Trading Standards, the new guidance is not to use them until they are repaired.
A statement on the Whirlpool safety website says: "If your tumble dryer is affected by this issue, then you should unplug it and do not use it until the modification has taken place."
Owners have been waiting up to a year for a free repair programme to be carried out.
Fires have been caused by excess fluff, which can come into contact with the heating element and so catch light.
One machine awaiting repair caught fire in London last August, causing a blaze in a tower block, which took 120 firefighters to bring it under control.
The dryers subject to the repair programme were manufactured between April 2004 and September 2015 under the Hotpoint, Indesit, Creda, Swan and Proline brands.
Background: Truth, fires and tumble dryers; are our home appliances safe?
Hotpoint - Online checker
Indesit - Online checker
Whirlpool freephone helplines: 0800 151 0905 for the UK, or 1800 804320 for the Irish Republic
Whirlpool has sent letters to 3.8 million owners of the affected dryers, but as many as 2.4 million have not responded. The company has re-written to them, offering to repair their machines.
A further 100,000 customers have registered, but not yet organised a repair.
"Since the launch of this campaign, safety has been our number one priority," Whirlpool said in a statement.
"We have consistently responded to the advice of Trading Standards and continue to do so. Trading Standards have now notified us that updated usage advice should be communicated to consumers and we are implementing this."
Trading Standards confirmed that the repair programme was the best way of resolving the problems.