The internal mechanism does most of the work. Traditional tap sets seal with a washer against a seat, and both are replaceable, which is why a well made traditional tap can be serviced for decades. Mixers use a cartridge, and the important question is whether that cartridge is a standard part that remains available. A mixer with a proprietary cartridge that is discontinued becomes unrepairable, and the whole fitting has to be replaced for a part that would otherwise cost very little.
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For a burst pipe or a serious leak, turn the water off at the mains tap before you call. If water is anywhere near power points, the switchboard or light fittings, stay clear and treat it as an electrical hazard. Do not enter standing water in a room with live power.
