Integrated appliances

Maintenance

Sir, I have a flat with a fitted kitchen ie cooker, fridge freezer, w/machine, dishwasher.
I have replaced the fridge freezer 18 months ago and I have replaced the w/machine less than 12 months ago.
The tenant has now emailed to say the dishwasher has a defective door lock and will not stay shut during its operation.
The property was purchased 12 years ago and has always been a BTL
This tenant has been in residence less than 2 years, with his wife. (2nd Jan 2019)
Tenants were on the 2017 RLA AST agreement and are now on a periodic.
The AST mentions nothing about who is responsible for the appliances, is it me? is it the tenants?
If it is me, can add something to an addendum to a new AST to make them responsible for all appliances.
Regards
Bob Clarke
p.s There has never been a problem with any of the appliances from previous tenants