coffeealex is it because water that is not circulating is more likely to leave limescale deposits? When you mention the service boiler do you mean the steam boiler? Does a full refresh of the boiler mean opening the hot water tap until x amount of water has come out?
It’s not “circulation” (as in termosiphon); it’s the fact that you have water with minerals in the boiler, but when you pull steam you are taking pure, distilled water out, and leaving the minerals in.
Service boiler = steam boiler (but since it can also be used for pulling hot water… it’s not just a ‘steam’ boiler)
Full refresh = pulling out all water from the service boiler and replacing it with (ideally) low mineralisation/demineralised water. This may involve draining the boiler via siphoning or opening a drain tap if draining via the hot water tap leaves significant amounts of water in the boiler.
coffeealex what do you use to measure the hardness? Is it test strips or a TDS meter? or other? also when deciding how often to change the filter on OZ what do you use as a guide? ie the change in hardness of the water been extracted after 3 months? 6 months etc In other words looking at whether the filters are still working efficiently? DaveC in one of his articles recommends adding a small amount of bicarbonate of soda to water to improve Ph ie make it more alkaline. Is this because acidic water is more damaging to espresso machines? And is the trade off of in reducing acidity whilst increasing tds slightly a good one in protecting your espresso machine? What would happen if you did not add bicarbonate of soda?
The only reliable method for measuring hardness is to use a GH (and KH) test kit. Usually in drops. A TDS meter is not particularly useful for a number of reasons, though it may provide an indication, especially if you know what is in the water (i.e. you have remineralised it yourself).
The duration of any filter - be it OZ, Zerowater, whatever else - depends on how much you use it and on the water you put in. Manufacturers provide instructions on how to assess the state of the filter.
Bicarbonate - partly used because of corrosion, but largely because it improves the taste of coffee. TDS by itself doesn’t mean much - what the ‘Dissolved Solids’ are is at least as important; water rich in chlorides will corrode, but not necessarily scale. Water rich in calcium or magnesium and (bi)carbonate will scale, but is unlikely to be corrosive. Both may have the same TDS.
If you don’t add “some” buffering agent (e.g. sodium bicarbonate), your coffee will taste worse and you are more likely to cause corrosion.
Bear in mind that on the issue of water mineralisation, there are things that are objectively clear and undisputed (e.g. presence of Ca and Mg + carbonates is necessary for scale to form), others that are “challengeable” (e.g. amount of dissolved chlorides that is ‘safe’ for a given material), and others still that are purely subjective: taste (e.g. @Rob1 finds coffee made from water containing magnesium sulphate tasting bad, I don’t).