How Long Does a Hot Water Cylinder Last?

How long each type of hot water cylinder lasts

Cylinders are not one product. The material, the working pressure and the way the water is heated all change how long the thing survives, so an average life expectancy across all of them is close to meaningless. These are the ranges an engineer would actually expect to see in London housing stock.

Notice that the low pressure copper cylinder, the old fashioned one that people are keen to rip out, is often the longest lived of the lot. It sits at the pressure of a tank in the loft rather than at mains pressure, so it is barely stressed, and copper tolerates hard water far better than it tolerates being blamed for poor shower pressure. If you are weighing the two designs against each other rather than dating the cylinder you already have, our comparison of unvented and vented cylinders sets out what each one gives you in pressure and what each one asks of you in maintenance.

• Vented indirect copper cylinder, fed from a cold tank: twenty to thirty years is normal, and plenty are still sound beyond that. They usually get replaced because somebody wants mains pressure, not because they have failed.
• Unvented stainless steel cylinder at mains pressure: fifteen to twenty five years. Serviced annually, the upper end. Never serviced, the lower end or worse.
• Unvented copper or glass lined steel cylinder with a sacrificial anode: ten to fifteen years, entirely dependent on whether the anode has ever been replaced. Once it is gone, the tank itself starts corroding.
• Direct electric cylinder heated only by immersion: the vessel may last as long as any other, but expect to be changing the immersion element itself far more often, particularly on a hard water supply.
• Electric thermal store, the Pulsacoil type found in flats: the vessel commonly outlives the electronics. Ten to fifteen years is typical before the control board, elements or pump make replacement the sensible option rather than the tank leaking.

Why hard water in London shortens cylinder life

Most of London is supplied with hard water drawn through chalk, and that has two separate effects on a hot water cylinder. Neither is dramatic on any single day, which is exactly why people miss them for a decade. Our longer piece on hard water and hot water cylinders in London works through the same damage component by component and says which treatments are worth paying for.

The first is scale. Above roughly sixty degrees, dissolved calcium comes out of solution and deposits on the hottest surfaces it can find. Inside an indirect cylinder that means the outside of the heating coil, which is the surface transferring heat from the boiler into the stored water. A coil with a layer of scale on it is an insulated coil. The boiler runs longer to heat the same tank, the recovery time stretches, and eventually you have a cylinder that takes the best part of an hour to do what it used to do in twenty five minutes. On an immersion heater the scale forms directly on the element sheath, the element cannot shed its heat into the water, it runs hotter than it was designed to, and the sheath fails. That is why immersion elements die young in London and live for years in soft water areas.

The second is corrosion. Stainless steel cylinders are vulnerable to chloride induced pitting, and the risk goes up with temperature, with stress and with chloride content in the water. When a stainless cylinder finally leaks, it is usually a pinhole at or near a weld seam or around a boss, not a general failure of the tank wall. It is not repairable and no sealant belongs anywhere near it. On glass lined and enamelled steel tanks, the defence is the sacrificial anode rod, a magnesium or aluminium rod that corrodes instead of the tank. It is a consumable. Nobody checks it, it dissolves away, and the tank quietly starts spending its remaining life unprotected.

Turning the store temperature down to avoid scale is not a free move. Stored water needs to reach sixty degrees to control legionella bacteria. Sixty is the sensible setting: hot enough to be safe, not so hot that scale formation accelerates.

What fails first on a hot water cylinder

It is worth separating the components that wear out from the vessel itself, because the two get confused and it leads people to replace a whole cylinder when a part would have done, or to keep repairing a tank that is finished.

Wearing parts are normal maintenance and no reflection on the age of the cylinder. The vessel leaking is the end of the road. The list below runs roughly in the order an engineer expects to meet them.

The one that fools people most often is the internal coil. If the coil develops a leak, mains pressure hot water can find its way into the heating circuit or the feed and expansion tank in the loft, and the symptoms look like a heating fault rather than a cylinder fault. An overflowing loft tank on a vented system is a classic sign of it. A steady drip into the tundish under a mains pressure cylinder is the other early warning, and it is worth understanding what a dripping tundish is telling you before deciding the vessel itself is finished, because the cause is usually a valve or the expansion side rather than the tank.

• Immersion heater element and its thermostat. Scaled, tripping, or simply not heating. A common and straightforward replacement.
• The temperature and pressure relief valve and the expansion relief valve on an unvented unit. Seats wear, grit gets under them, and the result is a drip into the tundish. Valves are replaceable items, but a valve that keeps failing is telling you something about the pressure and expansion side of the system.
• Motorised valves, the cylinder thermostat and the wiring that runs them. These sit outside the cylinder and have nothing to do with its age.
• Insulation. The sprayed foam jacket degrades slowly. The cylinder still works, but standing heat losses climb and the airing cupboard gets warmer than it should.
• The vessel. A weep from the body of the tank, rather than from a fitting screwed into it, means the cylinder is done. There is no repair for a corroded or pitted tank wall.

How to find out how old your cylinder is

Before deciding anything, find out how old it actually is, because guessing from how tired it looks is unreliable. A cylinder covered in dust and old pipe lagging may be twelve years old and perfectly sound.

Every cylinder carries a data badge, usually on the front of the jacket or on the top. It gives the manufacturer, the model, the capacity and either a manufacture date or a serial number that encodes one. Brands you will meet constantly in London include Megaflo, Gledhill, Telford and Heatrae Sadia. If the badge is unreadable, the paperwork usually survives somewhere: an unvented cylinder installed lawfully will have been notified to Building Control and will normally have a benchmark logbook, and that logbook also tells you whether anybody has serviced it since.

One sentence on the regulatory side, because it matters for who touches it: an unvented cylinder is work that must be carried out by an engineer holding the relevant unvented hot water qualification, and that applies to servicing as well as installation.

What shortens a cylinder and what adds years to it

Two identical cylinders installed in the same street in the same year can be ten years apart in condition. The difference is nearly always in the commissioning and the servicing rather than in the product.

The single biggest avoidable cause of early failure on an unvented cylinder is unmanaged expansion. Water expands as it heats and that expansion has to go somewhere. When the provision for it stops working, every heating cycle forces water out through the relief valve instead, the valve seat erodes, the tundish drips, and the whole unit spends its life cycling against a pressure it was not meant to hold. A cylinder in that state ages years in months. It is also the fault most often ignored, because a slow drip into a tundish does not flood anything and people learn to live with it.

What genuinely extends a cylinder is dull and cheap by comparison. An annual service, which includes testing the relief valves, checking the strainer, checking the expansion provision and inspecting the anode where one is fitted. A store temperature of sixty rather than seventy. Scale reduction on the incoming cold main in a hard water area. And getting a drip or a noise looked at when it starts rather than when it gets loud. If a cylinder in your property has never had one done, our walkthrough of what happens during an unvented cylinder annual service explains what the engineer tests and why each of those checks exists.

• Shortens it: no service since installation, an anode that has never been checked, a permanently dripping tundish, an immersion left running continuously in hard water, a store temperature set higher than it needs to be, and an installation that was never commissioned to the manufacturer figures.
• Extends it: annual servicing by a qualified engineer, correct expansion provision maintained, sixty degree storage, scale reduction on the cold feed, and replacing worn valves and elements promptly instead of nursing them.

When to replace a hot water cylinder rather than repair it

Age alone is not a reason to replace a cylinder. A twenty year old copper vented cylinder that is dry, quiet and heating properly does not need touching. The decision changes when the vessel itself is compromised or when the cost of keeping a unit alive stops making sense against what a new one would do.

Replace it when the tank body is weeping, when the water running from hot taps is discoloured or carries a metallic smell that cold water does not, when a stainless unit has pinholed anywhere, or when you are on your third relief valve and the underlying cause has been found to be the vessel rather than the valve. Replace it also when the unit is obsolete enough that spares are no longer available, which happens to control boards and proprietary parts long before it happens to tanks. The full set of signs that a cylinder needs replacing is worth reading through before you commit, and where the answer really is a new vessel, a hot water cylinder replacement is planned around the whole installation, the pipework and the discharge arrangement rather than around the tank on its own.

Repair it when the fault is in a component. Immersion elements, thermostats, relief valves, motorised valves and expansion provision are all serviceable items on an otherwise sound cylinder, and replacing a whole cylinder to cure a failed element is money thrown away. If somebody tells you a fifteen year old stainless cylinder that is heating correctly and not leaking needs replacing because of its age, ask them what specifically has failed. On a sealed system that is what an unvented cylinder repair exists for, and it is the correct answer far more often than a free replacement survey will suggest.

The honest way to make the call is to have the fault proved first. Our rate is fixed before we attend and the total depends on how long the job takes, so it costs the same to find out that your cylinder is fine as it does to find out that it is not, and knowing which one you have is worth more than a guess either way.

If water is coming from the body of the cylinder rather than from a joint or a valve, turn off the water supply to it and switch off the immersion and the boiler before anything else. A mains pressure cylinder holds a great deal of water and a pinhole does not stay a pinhole.