BUILDING BRIEFING:

Hot water supplies

In the second of a series about water supply and drainage, Peter Ryland, a surveyor specialising in residential buildings, examines hot water systems and problems that can arise.

Under the new HHSRS fitness tests, there should be adequate facilities for heating and washing in any dwelling. The property manager needs to be aware of the basic principles of these systems and the essential maintenance requirements ... or he could be in hot water.

Unlike other specific areas of building design and fit-out, the variables with respect to hot water and central heating systems are numerous. Is it a gas, electric, oil or solid fuel system? Is it water based or hot air, with radiators or vents, with freestanding boiler or back boiler, in a combi or standard tank system, with copper or plastic pipes or ducts?

The variables are too numerous to describe in an article of this type so we will concentrate on the standard forms, which provide the majority of heating systems.

Hot water system

The indirect hot water system is the basis of the majority of hot water systems in existence in the UK (Fig.1). A cold water tank (usually in the loft to give gravity feed) is supplied from the rising main. The tank feeds to the boiler, which circulates the water it heats through coils in a hot water cylinder, which in turn heat the water in the cylinder (again fed from the tank). The hot water supply can then pass on demand to the taps.

Because water expands, there is need for overflow vent pipes to the system to relieve any pressure build up in the system.

There is a building regulation requirement for cold water to be stored in any property, and so the supply to the boiler often comes from the cold water tank. But the 1970s saw the introduction of the combination ('Combi') boiler, which took its supply direct from the mains water supply. In this type of system the cold water tank merely feeds the cold water taps. In areas of variable water pressure, the combi-boiler initially had problems but improvements in design have made them far more efficient.

Further changes have been introduced, and now the building regulations require a condensing boiler to be used because it is more energy efficient. The boiler makes an improved use of the heat provided by the boiler thereby reducing emissions of fumes into the atmosphere.

Central heating system

Figure 1 shows a boiler producing not only the hot water but also the space heating. The boiler obviously has to be of a greater output due to its dual function.

Regulations for new installations now require each radiator to have its own thermostat to control the heat output in the various rooms, and for the system to be controlled by a time clock. Both of these make the system more cost and hence energy efficient.

A typical radiator installation is shown in Fig. 2. The heat input to the radiator is from the flow pipe through the thermostat and, having heated the radiator, the water returns through the return pipe and is then reheated by the boiler before returning to the flow pipe.

Common problems

The property manager should be aware of the various matters that can cause a failure or ineffective operation of a system. However, the most important issue, as now required by law, is to have the boiler checked once a year to ensure there are no gas leaks or CO emissions. A suitably qualified contractor must carry out this work, and a certificate issued accordingly.

The common problems are:

1) Fumes from the boiler - In addition to boiler leaks, mentioned above, this can be caused by a blocked flue. A balanced flue, which most wall-mounted boilers have, both draws air for combustion and disposes of gases. The unit on the outside of the wall must be enclosed by a guard, but it can become blocked by items being placed against it. A standard vertical flue (from a freestanding boiler) can be blocked by extraneous items entering from the top e.g. leaves. In both cases the effect is that fumes cannot escape properly and end up entering the property (and a build-up can kill). The property manager should ensure that the flues are kept clear.

2) Low temperatures in radiators - This may have a variety of causes:

(a) Overall low temperature could be caused by the low setting of the thermostat or the boiler. Both can be adjusted accordingly.

(b) Top half of radiator is cold. This is usually caused by an air lock in the top of the radiator. The air can be released by adjusting the valve in the top of the radiator to bleed off the air.

(c) Bottom half of radiator is cold. Over a period of time a residue can build up in the system and can be deposited in the base of a radiator. The only solution to this is to remove the radiator and pressure-wash it through.

3) Lack of flow in system can be caused by either:

(a) A blockage, see 2 (c) above, in the pipework rather than the radiator, which will necessitate the whole system being drained down and flushed through.

(b) A leak in the system. The latter can be as a result of:

- Damage to pipework due to the exposed position of the pipes to radiators; they can often be impacted upon and, especially in micro-bore systems, this can damage the pipe. Or, where pipework is concealed, it can be accidentally damaged by a misplaced nail.

- Ineffective joints to the pipework which, over a period of time, with expansion (during heating) and contraction (during cooling), can either come loose or move and result in leakage.

- Electrolytic action - most systems consist of copper pipes and steel radiators. An electrolytic action over a period of time between the two can cause the steel to corrode and pinholes form. When this happens the radiator needs replacement. Adding a rust inhibitor in the flow and return system can mitigate this effect.

Simplistically, sometimes the electric pump has been switched off since, although a system may be gas fired, the pump and timeclock are electrically powered.

It must be remembered that the above relates to standard gas boiler radiator systems with storage tank for water. The property manager should identify the system in all properties under management and ensure that he knows how the system functions.

Although he will not be qualified to repair a faulty system, there is a simple check list he should have so that if a tenant informs him of a problem he can identify, as far as possible, the nature of it. He can then take action to ensure that it does not get worse until the engineer calls or, if simple, can be remedied without the need for an engineer.

Other than a minor fault, e.g. pump switched off, neither the property manager nor the tenant should endeavour to remedy a problem. Always call a qualified engineer.

Combi boilers - an introduction

The combi boiler, unlike the traditional boiler, takes its cold water supply directly from the mains water supply producing hot water on demand. Therefore, this type of boiler does not require a hot water cylinder in the airing cupboard or a cold water cistern and small header cistern in the loft. All the major components are housed in one unit, which makes them very convenient to the installer, and they are often fitted in the existing airing cupboard, replacing the hot water tank. They are especially suitable for smaller households although the latest models seem more capable than their predecessors.

A combi boiler heats water on demand for taps and showers. Consequently the flow is determined by the temperature required, but is not limited by tank size. This high pressure/ low flow can mean that a bath takes longer to fill but is perfect for showers and dispenses with the need for shower pumps which might be necessary in a conventional system with a low pressure head (provided by gravity from the cold water tank). However, since the system is fed directly from the main, flushing a toilet may lead to the hot water temperature fluctuating.

An immersion heater cannot be used alongside this system as there is no cylinder for it to go in.

Since all taps/showers/WCs are fed with mains pressure, in old installations there may be a need change tap washers/re-seat taps, change WC ball-cock to high pressure ones, or fit high pressure thermostatic controls to showers.

The combi boiler is part of a pressurised system, and will require occasional re-balancing. For example, from personal experience, on Easter Sunday when you bleed a radiator and the boiler shuts down because the pressure is too low. A flexible filling loop, and instructions, should be provided when the boiler is installed. All you have to do is remember where they are!

The Landlord's check list should include:

1. Where is the time-clock?
2. Where is the boiler pump switch?
3. Is the flue accessible?
4. Where is the stop valve?
5. Where is the 'off' switch for the boiler?
6. Give tenant written instructions for the system's correct operation, including bleeding radiators if necessary.