I see there has been much discussion on this topic, but I am left a little confused. I currently have a 2 year old home on a community well that has tankless water heater. Ever since we moved in we are constantly cleaning small pieces of rock out of the screens of the faucet heads. To try and combat this, I installed a whole house filter...purchased at Lowe's. We contine to have the rocks despite the filter. Is this something in my lines or coming from the well? Will the whole house filter <$100 products effectively filter this type of sediment. Sorry if this is a duplicate question and appreciate your replies!
It could be mineral deposits created in the high heat of the tankless and with hard water. You might want to have your water tested for hardness and maybe install a water softener. Like deposits on the bottom of your teakettle, except the WH heats a LOT more water.