Fresh lemon juice works if you do not want vinegar in the house smell. Squeeze enough to make a few tablespoons and top up with water to cover the scale, bring to a boil and let it sit fifteen to twenty minutes. The scale will soften and wipe off easily and... no scrubbing needed most times. Rinse well and do one plain boil and dump.
How often depends on how crusty your tap water is. For heavy scale do it every week until it calms down, otherwise every month keeps things tasting clean.
