The firm's vice-president apologised for the "worry and inconvenience" caused to customers.
The company has added 21 additional Hotpoint and Indesit models to a product recall it started in January, saying there is an issue with the heating element of machines in warmer washes.
Whirlpool said it was contacting affected customers whose details it has, and urged anyone who thinks they have one of those listed to use the "check my model" button on the website or call the customer service team on 0800 316 1442.
Concerned customers are warned to avoid risks by unplugging their machine completely, but anyone who does continue to use it is advised to only use cold water cycles of 20 degrees Celsius or lower.
Whirlpool VP Jeff Noel said: "I want to apologise sincerely for the worry and inconvenience I know this will cause, especially during these difficult times.
"I'd also like to reassure you that we are working as quickly as we can to provide solutions to affected customers as soon as possible.
"Nothing is more important to us than the safety of our customers, and working quickly to remove the affected appliances from customers' homes is our number one priority."
Whirlpool said it is following Government guidelines and has strict health and safety processes in place when deploying engineers to homes to carry out replacements or repairs. It added that contactless delivery and removal of affected appliances is also an option.
Since launching the recall at the beginning of the year, Whirlpool said 210,000 people had registered their appliances.
The latest affected models are: WMAQB 641P UK, WMAQB 721P UK, WMAQB 741G UK, WMAQB 741P UK, WMAQF 621P UK.L, WMAQF 641G UK, WMAQF 641P UK, WMAQF 721P UK, WMAQG 641G UK, WMAQG 641P UK, WMAQG 721P UK, WMAQG 721P UK.M, WMAQG 741P UK.M, WMAQL 621P UK, WMAQL 641P UK, WMAQL 721A UK, WMAQL 721P UK, WMAQL 721P UK.M, WMAQL 741G UK, WMAQL 741P UK, WMSAQG 621G UK