For a trade buyer, the practical upshot is that unvented spares are not interchangeable with vented ones. A pressure relief valve rated for an unvented system is a specific, tested part, not a generic valve that happens to fit the thread. The same goes for the expansion vessel, sized to the cylinder's stored volume, and the tundish and discharge pipework that safety fittings rely on to work as intended. Buying the wrong-rated part to save time on a job is a false economy at best.
Scale does not stop at heating elements. It builds inside pipework, gradually narrowing the internal bore and reducing flow rate at outlets that used to run fine. It clogs the fine mesh in shower heads and tap aerators, cuts the working life of washing machines and dishwashers, and leaves the visible white residue on taps, glass shower screens and kettles that most people in a hard-water area recognise on sight. None of this is a design fault in the appliance; it is simply what hard water does over months and years of normal use.
On a real job, the choice usually comes down to duty and visibility. A washing machine or dishwasher connection tucked away and rarely inspected is a stronger case for braided, precisely because nobody is checking it every month. A short, accessible, low-duty connection under a basin might be perfectly well served by a standard rubber hose at lower cost. Higher-pressure systems, including unvented cylinders and combination boiler connections, lean towards braided as standard practice, given the sustained pressure they run under.
For anyone new to the category, the buy plumbing parts online worth understanding are the resin tank itself, the brine tank that holds the salt, and the control valve that manages the whole cycle, timing when regeneration happens and how much water and salt it uses. Cheaper units tend to run on a fixed timer regardless of actual usage; better-specified ones meter flow and regenerate only when the resin genuinely needs it, which uses less salt and less water over a year.
A storage or cylinder-based electric water heater works differently. It heats a fixed volume ahead of demand and holds it at temperature, ready to deliver decent flow to more than one outlet at a time. The trade-off is recovery time: once the stored volume is drawn down, the immersion element needs time to bring the next tankful back up to temperature. For a family bathroom, a kitchen and an en suite all wanting hot water within the same hour, a cylinder with enough capacity usually outperforms an instantaneous unit trying to keep pace.
A braided hose is built around an inner core, usually rubber or PTFE, with an outer layer of woven stainless steel strands wrapped tightly around it. That braid does not stop the core from ageing, but it does two useful things: it takes on most of the mechanical load and abrasion resistance, protecting the inner core from damage, and it gives a visible early-warning sign if something is wrong, since a failing braided hose often bulges or shows a strand starting to fray before it lets go completely. Rubber hoses tend to fail with far less warning.