Concealed cisterns sit behind a wall or inside a duct, with only a flush plate visible in the finished bathroom, and that single design choice changes almost everything about how a plumber approaches a repair. There is no lid to lift and no tank to inspect at a glance, so the whole job starts with getting through the access plate before any diagnosis can begin.

A close-coupled cistern bolts directly onto the back of the pan with no visible pipework between the two. Because the outlet on the cistern base sits directly above the inlet on the pan, the flush valve or siphon needs a shorter outlet and often a rubber doughnut washer to seal the joint rather than a length of pipe. Fill valves on close-coupled units tend to be shorter in the body too, since there is less depth inside a compact tank.

Locating the access plate is the first practical step, and it is not always where it looks like it should be. Some concealed frames put the service access behind the flush plate itself, which simply hinges or unclips forward once the buttons are removed, while others use a separate panel elsewhere on the same wall or in an adjoining space such as an airing cupboard. Getting this wrong before checking the frame manufacturer's layout wastes time working into a wall that did not need opening.

When a full lever replacement is needed, the fitting type has to match what is already there. Side levers, which mount through a hole in the side of the cistern, come in different thread diameters and in both metal and plastic bodies, and the arm length inside the tank needs to reach the flush valve or siphon without fouling the tank wall. Levers that mount through the lid, more common on close-coupled and concealed designs, connect via a spindle rather than a side arm and are not interchangeable with side-lever fittings.

Before ordering, measuring the fixing centres and checking whether access beneath the pan is realistic will settle top-fix versus bottom-fix and the correct spacing in one go. Plumb2U Epsom stocks both top-fix and bottom-fix hinge sets and soft-close spares across the common fixing centres, at trade prices, so plumbers replacing seats across several jobs a week can order to the measurement rather than to a guess. As a plumbers merchants stocking both fixing types in depth, Plumb2U's seat spares range covers most of what a trade buyer will meet on a typical round.

Start with the fill valve. This is the mechanism that lets water into the cistern after a flush and shuts off once the tank reaches the correct level, usually via a float or a diaphragm. When a fill valve wears, the most common signs are a hissing or trickling noise that continues long after the cistern should have stopped filling, a water level creeping up to or past the overflow pipe, or a float arm that no longer rises high enough to trigger shut-off. Mineral deposits inside the valve seat are often the culprit, particularly in hard water areas, and once the seal degrades a full replacement is usually more reliable than trying to clean it out.