Float & fill valve replacement in Macclesfield

The traditional design is a ball on an arm — the ballcock — which rises with the water level and closes a washer against a seat. It fails when the washer perishes, when the pivot wears, or when the ball itself splits and part-fills with water so it can no longer float high enough to close. That last one is easy to spot: a ball that sloshes when you shake it is finished.

Modern fill valves work on a diaphragm and either a float cup running up the valve body or a short arm. They are quieter, they shut off more positively, and they fail differently: the diaphragm hardens and lets a trickle past, so the level creeps up until it reaches the overflow. On a modern cistern that overflow discharges internally into the pan, which is why the failure is silent and expensive.

Pressure matters when choosing a replacement. Valves are made in high-pressure and low-pressure versions with different orifice sizes, and fitting the wrong one gives you either a cistern that takes five minutes to fill or one that hammers and fails early. A gravity-fed loft tank system needs the low-pressure type; a mains-fed cistern needs the high-pressure one.

In storage tanks — the cold water cistern in a loft, or the small feed-and-expansion tank for an open-vented heating system — a failed float valve is more serious, because the overflow discharges outside and a large tank can put a lot of water down a wall before anyone notices. Both should have their valves checked when anyone is up in the loft for other reasons.

Where a valve is noisy rather than failed, a fitted silencer tube or a modern quiet-fill valve solves the water-hammer thud you can hear through the house every time the toilet refills.