I have found the following useful info; SIMAC who produce the Stirella have gone into administration but have been taken over by De Longhi who now honour the warranty (advised by John Lewis). For cleaning I have been advised two options, both assume use of the CalStop additive.
1. If you are only seeing brown staining then it may be a build up of the CalStop. To correct this, fill the resevoir with tap water and run on continous steam for two cycles then revert to using the CalStop once every 3 to 4 fills.
2. If you are seeing scale and staining then DO NOT USE standard descaler. Add 5 vials of CalStop and set the iron to hot with a continous steam cycle. CalStop is a preventattive measure and not a descaler as such but I have spoken to a sales rep at De Longhi in the UK who advised this will aslo clean the machine. Once this has completed, fill the reservoir and repeat the steam cycle again and revert to using CalStop only once every 3 to 4 fills (based on using the iron 2-3 times a week)
**USING STANDARD APPLIANCE DESCALER WILL BREAK THE MACHINE
Roberto Alonso
January 2010