Yes, a faulty float valve is one of the most common reasons water runs from an overflow pipe. If the valve does not shut off when the cistern is full, water keeps coming in and the extra spills out through the overflow. The good news is that these valves can often be repaired or replaced fairly simply.
How a Float Valve Controls the Water Level
A float valve, sometimes called a ball valve, lets water into a cistern and stops it at the right level. Older types have a plastic or copper ball on the end of a metal arm. As the water rises, the ball floats up and pushes the arm, which closes the valve.
Modern toilets often use a fill valve instead. This works on the same idea, but the float sits on a vertical post or inside a small cup next to the valve. When the float reaches a set height, the valve shuts and the flow stops.
If any part of this system fails, the valve may stay partly open. Water then keeps trickling in until it reaches the overflow.
What Goes Wrong Inside the Valve
Inside most float valves is a rubber washer or a flexible diaphragm. This presses against a small opening to stop the water. Over time it can wear, harden or split, and water may then seep past even when the float is up.
A split float is another cause. If water gets inside the ball, it sinks lower and no longer lifts the arm high enough to close the valve. Grit, scale or tiny bits of debris from the pipes can also lodge in the valve and stop it sealing.
Water pressure can affect how well a valve shuts off too. A valve not suited to the pressure in your home may struggle to close fully.
Toilet Cisterns and Loft Cisterns
In a toilet cistern, a failing fill valve often shows as a faint hissing sound or a constant trickle into the pan. In a loft cold water storage cistern, the first sign is usually a drip from a pipe high on an outside wall.
Loft cisterns can be harder to check, as they are often in tight spaces with poor lighting. It is best to leave inspection to someone who can reach it safely.
Repair or Replace the Valve?
If the valve is fairly new, a plumber may be able to fit a new washer or diaphragm, clear out debris or adjust the float height. A split float can sometimes be swapped on its own.
If the valve is old, worn or a type that is hard to get parts for, replacing the whole valve is often more reliable. A modern valve may also be quieter and easier to adjust. You can find out more about getting a dripping overflow pipe fixed on our service page.
If you suspect a float valve is behind your overflow problem, Emergency Plumber Swindon can check it and explain what is needed. Call 01793 569521 for help in Swindon.