I have a problem with WCs, generally with how they flush, and specifically, when they stop flushing. I tried to fix a broken flushing mechanism a few years ago and ended up, after 3 visits to the DIY superstore, calling out a plumber who charged me £30 to assemble the bits back together and make it leak-proof. The new mechanism developed the same problem a few years later. Armed with experience, and remembering the tears of frustration, I called a plumber straight away (a different one) and he charged £140 to replace a 50p bit of plastic membrane in the siphon. I didn’t sleep at night for years, and used buckets, to avoid stressing the siphon mechanism, until now.

Siphons

The predominant method of flushing UK WCs uses the siphonic principle. How does that work? A cistern fills with cold water, (usually, I will mention this again), controlled by a ball cock. This is not a reproductive organ, but a hollow plastic or copper sphere that floats in the cistern and shuts off the water flow when it reaches a preset level, and was invented by Thomas Crapper. His admirers have coined a well-known phrase in his honour. Once it reaches the level an amount of water in the cistern, usually around 6 litres, is available for flushing. The siphon itself is an inverted U-shaped plastic tube. This fills with water as the cistern is filled, and then sucks the contents of the cistern to send it to the WC bowl for flushing purposes. The sucking is initiated when you press the handle on the cistern. This lifts a water-covered flexible membrane, which is inside the inverted U-shaped plastic tube. A quantity of water is elevated to the top of the inverted U and initiates the siphonic action. Once the water has been sucked out of the cistern it refills until the ball cock shuts off the water supply again. During this period the plastic membrane that lifted the water flexes in the opposite direction to allow water back into the the siphon. It has to flip and flop backwards and forwards many times a day and eventually, because it is just a thin and flexible piece of plastic about half a millimetre thick, it starts to crack. The lifetime of this is around ten years before it needs replacing. To replace it, however, the cistern has to be emptied, the siphon and ball cock, dismantled, the membrane replaced, the whole lot reassembled and reconnected to the water supply. Although the replacement part costs 50p, the plumber’s time can cost a great deal more. And if you try to do it yourself, hours of frustration, broken bits of plastic plumbing, water everywhere, a strained back, stripped threads, skinned knuckles, tears and Basil Fawlty episodes with a twig snatched from the garden.

How do you know when a siphon needs replacing? Simple, when you press the handle on the cistern, instead of lifting water to the top of the inverted U-shaped tube, the membrane just lets the water pass by and nothing happens by way of flushing. What happens if the water entering the cistern isn’t cold? Instead of lasting ten years, the membrane lasts three or four years. But why would the water not be cold? When the cold and hot water pipes in the system are too close together and the cold water pipe is heated by the hot water pipe!

This design of flushing mechanism is, I believe, peculiar to the UK. It has advantages such as it’s inexpensive, and is leak-proof when it fails. But the down-side is it’s horribly expensive to replace a bit of membrane.

Flapper Valves

I discovered an alternative to the siphon flushing mechanism recently. This is common in North America and Europe and has now been introduced into the UK. The principle is much simpler: when you depress the flush handle (or button) on the cistern, a flapper valve is opened which allows the water in the cistern to fall, under gravity, into the bowl. The advantages are there is no flimsy membrane to wear out, and the flap can be replaced without draining and dismantling the cistern. A secondary advantage is that the pressure of a finger can activate the flush, because you are not lifting water, just opening a flap. The downside is that if the flap wears and starts to leak, it will not be immediately obvious because the water will drain into the toilet bowl.

This came as a revelation to me. I fitted one recently, in a couple of hours, and am now freed from the tyranny of plumbers, mental and physical scars, siphons and broken membranes! (The ball cock has also been replaced with a compact float that fits into the cistern without hours of fiddling and adjustments). I commend this to UK toilets everywhere.