Water usually drips from an overflow pipe because a cistern somewhere in your home is filling higher than it should. This is often linked to a faulty float valve or inlet valve that is not shutting off properly. The first job is to work out which cistern the pipe comes from.
What an Overflow Pipe Is For
An overflow pipe is a safety outlet. If a cistern fills too high, the extra water runs out through the overflow instead of spilling over the top and into your home.
Water Regs UK explains that every cold water storage cistern must have an overflow pipe that discharges somewhere safe and easy to see. That is why many overflow pipes poke out of an outside wall, so a drip will catch your eye. In other words, the dripping pipe is doing its job and warning you of a problem.
Which Cistern Could Be Causing It
Many homes have more than one cistern, so the position of the pipe can give a clue.
A pipe just outside a bathroom wall often comes from a toilet cistern. In many modern toilets, the overflow runs inside the pan instead, so you may see a thin trickle running down the back of the bowl rather than outside.
A pipe high up near the eaves may come from the cold water storage cistern in the loft. This tank feeds some taps and the hot water cylinder in older systems.
Some homes with an open-vented heating system also have a smaller feed and expansion cistern in the loft. This tops up the heating water, and it has its own overflow too. If you are unsure which one is the source, a plumber can trace it.
Why the Water Level Rises Too High
The most common cause is a valve that lets water in but does not close fully. This can happen when a washer wears, a float gets stuck or damaged, or grit stops the valve sealing. The float arm may also be set too high, so the water reaches the overflow before the valve shuts off.
Less often, a problem with a hot water cylinder or heating system can push water back into a loft cistern. This is harder to spot and may need a closer look.
Why It Is Worth Getting It Checked
A small drip may not seem serious, but it can waste a lot of water over weeks and months. If you are on a water meter, it can add to your bills. Constant water can also stain walls, damage brickwork or create icy patches on paths in winter.
A plumber can find the source, adjust or repair the valve, and check the cistern is in good condition. Our page on overflow pipe repair in Swindon explains how this is usually handled.
If you have noticed a steady drip from an outside pipe, Emergency Plumber Swindon can take a look and help you find the cause. Call 01793 569521 to talk it through.