Understanding your water system

The layout of most water systems is a mystery to many householders. Get to know how the plumbing system works and you will be able to save on plumbing and emergency repair bills.

Domestic plumbing systems, and the ways in which they work, often seem quite baffling. So when something goes wrong, there is always the temptation to call in a plumber, rather than venture into unknown territory,

In many cases, however, a visit from the plumber is an unnecessary expense. Although plumbing installations vary a great deal from house to house, all follow the same basic set of rules and can usually be sorted out with little difficulty.

Where the water comes from

Cold water comes to your house from the water authority mains via a smaller, service pipe. This pipe may have been installed specifically to serve your house or you may share it with a neighbour. Either way, it will be controlled by a water authority stopcock somewhere on the edge of your, or your neighbour’s property. The stopcock is sunk below ground (usually about a metre) and is encased in brickwork, concrete, or a stoneware pipe to provide access. To mark the site, a small cast-iron casing is usually fitted at ground level.

From here, the service pipe runs to your house and becomes known as the rising main. At the point where it enters, a further stopcock – known as the consumer’s, or house, stopcock – is fitted. This one is your own property and, because it controls all water entering the house, it is as well to know where to find it.

The most common place is under the kitchen sink, where a branch of the rising main directly supplies the kitchen cold tap with drinking water. The other most likely locations are under the stairs, or below floorboards immediately inside the front door.

The cold storage tank

After the branch to the kitchen cold tap, the rising main runs to a cold storage tank or cistern. The water pressure in the mains allows this to be mounted high up in the house, normally in the roof space. Older storage tanks are made of galvanized iron, which is both heavy and prone to rust. These have now been replaced by the lighter, more hygienic, plastic tanks which are maintenance-free.

The storage tank helps to iron out irregularities in the main supply and also provides an emergency reservoir if the supply is cut off.

The rising main delivers water to the top of the tank via the control of a ball-valve. At the base of the storage tank you will find the main water outlet. The stored water flows through here under the pressure of gravity and then branches off to supply the rest of your house’s water requirements. These will include the lavatory, the bathroom cold taps and the hot water cylinder.

A stopcock is normally fitted somewhere near the outlet, so that you can turn off most of the water, but still leave your kitchen cold tap in operation to supply the family’s needs while you are working.

The hot water supply

In household plumbing, cold water is converted to hot either directly or indirectly. Direct heating means that the cold water comes into direct contact with a heater – normally a boiler or an electric immersion heater – then flows straight to the taps.

With indirect heating – usually combined with central heating – the water heated by the boiler is itself used to heat up fresh cold water. In this system, the two hot water circuits are separate and heat is transferred from one to the other by means of a heat exchanger.

The hot water cylinder, a copper tank heavily insulated to guard against heat loss, is common to most hot water installations.

In direct systems, it houses the electric immersion heaters – if fitted – and acts as storage tank to keep your hot water supply as constant as possible. In an indirect system, the cylinder has the additional function of housing the heat exchanger.

The direct flow

The flow of water in both direct and indirect systems relies on the principle that hot water always rises above the cold water around it. So, in a direct system, the flow starts with cold water running to the base of the hot water cylinder.

If immersion heaters are fitted instead of a boiler, the flow is greatly simplified. The water runs from the storage tank to the base of the hot water cylinder and is heated: it then rises straight out of the cylinder and on to the hot taps.

The great disadvantage of direct systems is that water, when it is heated above 60 C (140 F) – or 80 C (180JF) in soft water areas – deposits scale similar to kettle fur.

The scale can block up pipework and boilers alike unless adequate precautions are taken. These include keeping the water temperature down below the ‘scaling point’ and using scale-inhibiting additives in your cold storage tank.

The indirect flow

The easiest way of understanding an indirect hot water flow is to visualize two independent ‘loops’ of water. The first loop consists of the water used to feed the hot taps.

This flows from the cold storage tank to the base of the hot water cylinder, where it comes into thermal contact with hot water on the other loop (via the heat exchanger). As the water is heated, it rises out of the cylinder and on to supply the taps.

The other loop supplies the boiler, heat exchanger and – if fitted – the radiators. Here,, fresh water flows to the base of the boiler from either the storage tank or from another separate tank, known as the ‘expansion tank’.

Once in the boiler, the water is heated and then rises out to feed the heat exchanger and radiators. After the water has given up its heat, it flows back to the boiler to be heated again.

Because the water in this loop is hardly ever changed, the problems of scaling are greatly reduced. The first time it is heated, the water gives up its scale: from then on, it is unable to do further damage.

The expansion tank

The indirect arrangement works best when an expansion tank is fitted to supply the boiler loop. This makes the loop almost completely independent of the one supplying the hot taps.

The tank is supplied with water from the rising main via another ball-valve. So, if the loop needs topping up with water because of a leak, the process is automatic. In practice, changes in the water level inside the expansion tank are barely noticeable.

If you are unlucky enough to have a leak or a burst pipe, your first step must be to cut off the water supply. Do this as near to the offending area as possible so that inconvenience is kept to a minimum. Hot water pipe or tap: Look for a stopcock on the pipe which runs into the base of the hot water cylinder or boiler. Before you turn it, make sure that all heating apparatus is off.

To guard against the build-up of high pressures in the hot water system, overflows or vents are fitted.

In a direct system, only one pipe is needed. This runs to the top of the cold storage tank, either from the crown of the hot water cylinder or from a branch off the hot water service pipe.

In an indirect system, an additional vent is installed at the top point of the primary circuit.

Turning off the hot water

Whatever your hot water system, the hot water which reaches the taps comes from the top of your hot water cylinder.

Cold water pipe or tap: Trace back along the relevant pipe until you come to a stopcock. If there are none between the burst and the cold storage tank, you will have to block the tank outlet. To do this, nail a cork slightly larger than the outlet hole on to the end of a piece of timber. By ‘remote control’, you can now insert the cork into the outlet and prevent further water from leaving the tank.

The cylinder beneath.

So, if you cut off the cold water supply at the base of the cylinder, no further hot water will rise from the top. Most hot water cylinders have a stopcock for this purpose, fitted at the cold water inlet. Those that do not invariably have a stopcock somewhere on the pipe between the inlet and the cold storage tank. Before touching this stopcock make sure that all heating apparatus is turned off.

Wet central heating

Wet central heating, in which hot water is used to heat the house via a system of radiators, adds an additional complication to plumbing installations. But if you can imagine the radiators and their pipes as being part of the boiler ‘loop’ in a basic hot water system, the whole thing becomes easier to understand.

In the garden: If possible, turn off the water authority stopcock. Leaking galvanized storage tank: A leak here will probably be due to a rust spot which has eaten its way right through the metal. Once you have drained the tank and tied back the ball valve, you can turn off the house (rising main) stopcock.

Should the outlet prove impossible to block, drain the tank instead. First tie back the ball valve to a piece of timber stretched across the tank : this will stop fresh water from entering. Now, turn on your bath, or washhand basin cold tap, until the tank is fully drained.

Cure the leak by drilling out the rust spot and fitting a nut and bolt into the hole. Burst lead pipe: A crack in a lead pipe can be temporarily stopped by ramming in a matchstick and then rubbing the area with candle wax. Follow this by binding up the repair with strong tape and keeping any relevant stopcocks at half pressure until a proper repair can be done.

Some older installations work on the direct principle in which hot water heated by the boiler flows to the radiators as well as to the hot taps. Because this system is uneconomical and causes scaling, it has been replaced by indirect installations.

Here, the water which flows to the radiators is on a pump-driven loop like the one used to supply the heat exchanger. Consequently, it is always fairly hot and requires less heating, which in turn makes it far more economical than a direct system.

In some indirect systems, the water which supplies the boiler loop is drawn direct from the storage tank. But most incorporate a separate expansion tank to keep the loop independent of the rest of the water supply.

Radiator systems

The pipework used to supply the radiators may take one of two forms. In the simpler, one-pipe system, hot water flows from the boiler to each radiator in turn and then back to the boiler again. Although this cuts down the amount of pipework needed, it allows hot and cooled water to mix near the end of the run. Consequently, the last radiator in the run often remains cool however hard the boiler is working.

In the two-pipe system, the pipework is arranged so that cooled water leaving the radiators cannot mix with the hot water entering them. The radiators therefore heat up faster, as well as remaining at the same temperature.

Sizing of inward and outward piping in the radiator circuit is matched to the given radiator load. At the boiler a 28mm width supply pipe may be used, this reducing to 22mm at the branch-off point of each radiator bank. Tubing 15mm in diameter is then used to connect the first radiator, and to continue the supply run in the case of a two-pipe system.

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