The manufactures provide a suggested preventative maintenance routine in their Operation Manuals.
The interval may vary based on usage and water quality.
Besides reviewing the Steamist manual for their recommended maintenance, you may also wish to add a Water Conditioning system to your steam boiler installation. It is callled ScaleOut System (SOS)
click here for more info SOS Water Treatment
Also, for cleaning the tank and components, our ScaleBuster product works extremely well.
click here for more info ScaleBuster