There is the visible exposed cistern and the concealed in-wall cistern found in modern bathrooms behind a stud wall (in Switzerland often a Geberit system). In both cases the function is the same: after flushing, the fill valve lets in fresh water until the float reaches the set level. Pressing the button opens the flush valve and releases the water – on modern cisterns with a saver button for the small and one for the large volume.
The most common fault is a cistern that runs continuously: water trickles quietly into the bowl non-stop. The cause is usually a scaled or worn flush valve or a defective fill valve that no longer closes cleanly. This is not only annoying but causes considerable water loss over weeks. Other typical cases are a jammed or broken flush plate, a weak flush or a cistern that no longer fills at all.
To repair it, the plumber first shuts off the angle valve and empties the cistern. On the exposed model the valves are easily accessible and quickly swapped. On the concealed model the flush plate is removed, the faulty valve taken out via the inspection opening and a matching spare fitted – for common systems spare parts are readily available. The water level is then adjusted and tightness checked.
A typical repair takes around 30 to 60 minutes. As a guide, replacing a fill or flush valve costs around CHF 150 to 350 including call-out, material and labour (no guarantee, depending on accessibility and system). A new, complete concealed cistern including installation is considerably more expensive, as the stud wall must be opened.
What to watch for: if the cistern runs continuously, don't wait – the creeping water loss adds up on the bill. For concealed systems it helps to know the brand and type so the right spare is on hand. In hard-water regions, occasionally descaling the valves extends their life.