FROST AND THE

HOT WATER SYSTEM

A well designed hot walcr cylinder storage system provides any home with its best insurance against the risk of frost damage. No matter how effectively a cylinder is lagged, some warmth will always be conducted along the pipework and rise up into the roof space, giving a measure of protection to the cold water storage cistern. This again emphasizes the importance of having the cold water storage cistern sited directly above the hot water cylinder and not insulating the area immediately below the cistern.

A packaged plumbing system, in which the storage cistern and hot water cylinder are combined in one unit, gives virtually total protection to the cistern and the pipes in the immediate vicinity as long as the water in the cylinder is hot.

Boiler explosion

One of the great fears, particularly where water is heated by means of a boiler, is still that of a boiler explosion – and people often worry a great deal more about their hot water system during cold spells than they do about the cold water supply pipes. However, if you can understand the cause of boiler explosions and take simple and straightforward precautions to avoid them, you need never have a moment’s anxiety over this happening.

A cylinder hot water system is. in effect, a large ‘U’ shape tube with the boiler at its base and the vent pipe and open storage cistern providing the two open ends. Provided the pipe run between the boiler and the vent pipe – or the boiler and the cold water storage cistern – is not obstructed, there can be no dangerous build-up of pressure. A spring-loaded safety valve, positioned on either the flow or return pipe in the immediate vicinity of the boiler, provides a final line of defence.

Boiler explosions usually take place when a house is reoccupied after having been empty during a prolonged spell of severe weather. The existence of the normal protective measure lagging – will not add warmth to the plumbing system; all it can do is slow down the rate of heat loss. While the house is occupied, this is all that is needed; the fabric of the house is warm and water is constantly being drawn off and replaced. When the house is empty, however, the fabric chills off and water stagnates in the supply and distribution pipes. If a spell of cold weather intervenes, a severe freeze-up is inevitable. Plugs of ice will form in the upper part of the vent pipe and in the cold water supply pipe from the cistern to the cylinder. Ice may even form in the boiler itself and in the pipes between the boiler and the cylinder.

The real danger comes if. under these circumstances. the boiler lire is lit. Water in the boiler will heat up. but it will not be able to circulate or expand. Internal pressure will build up until. ultimately, something gives and releases it. In an instant the superheated water in the boiler will turn into steam, with many thousand times the volume of the water from which it was formed, and the boiler will explode like a bomb with equally devastating results.

Cylinder implosion

Boiler explosions are. happily, an extremely rare occurrence. Cylinder implosion or collapse – is rather more common in frosty weather: this is particularly likely to occur when the boiler is allowed to go out at night. Small plugs of ice form in the upper part of the vent pipe and in the upper part of the cold water supply pipe to the cylinder. The warm water in the cylinder and boiler cools and contracts, producing a partial vacuum. Cylinders are not constructed to withstand external pressure and. when this occurs, the storage cylinder will collapse like a paper bag under the weight of atmospheric pressure.

The way to avoid either cylinder collapse or boiler explosion is to keep the boiler lire alight and the house warm during cold weather, although this may be difficult if you have to go away for any length of time.

Useful precautions

If you have a reliable automatic central healing system, the best precaution is to leave it turned on at a low setting or under the control of a Trost-stat’. Keep internal doors open to allow warm air to circulate through the house and partially remove is to be used the flap to the loft space to permit some warmth to penetrate to this area as well.

You may not be able to control your central heating system in this way; but both it and the primary circuit of your indirect hot water system can be protected by the addition of a proprietary anti-freeze solution. Don’t, however, be tempted to use the same anti-frceze you put in your car radiator, since it is quite unsuitable for central heating systems. There is a corrosion inhibitor available which, when introduced into the system. will afford protection against up to — 1]’C. Below that temperature any ice which forms will tend to be soft and mushy – and therefore unlikely to cause damage. Anti-freeze solutions. suitable for domestic central heating systems, are available which give protection against even more severe conditions.

The only other really safe precaution is to drain the domestic hot and cold water systems. Turn off the main stopcock and empty the system by opening the draincock immediately above it if there is one. Remember to attach a length of hose and run it to the sink or outside, otherwise you will flood the room. Open all the taps as well until water stops running. The hot water storage cylinder and with a direct hot water system the boiler will still be filled with water. With a direct system this can be drained by connecting one end of a length of hose to the draincock beside the boiler and taking the other end to the sink or outside. Open the draincock and wait while the boiler empties. If you have an indirect hot water system – or a direct system heated only by an immersion heater -the appropriate draincock will be located by the cylinder, probably at the base of the cold water supply pipe which feeds it.

Warning ‘Always remember to switch off the immersion heater before you drain the system.

There is one final precaution you can take: before you leave the house, flush the WC cistern to empty it and throw a handful of salt into the pan. When you return home, remember the system is empty – and make sure you refill it before lighting the boiler fire. To reduce the risk of air locks forming as you do this, connect one end of a length of hose to the cold tap over the kitchen sink and the other end to the boiler draincock. Open up the tap and the draincock and the system will fill upwards, driving air before it.

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