Average lifespan of hot water cylinders

[Kat Achterberg]

Hi all,

I’ve had a question by a customer regarding the average lifespan of hot water cylinders. The cylinder in question is 13 years old and apparently in good order. I have not seen it myself and don’t know the brand or model. The question now is whether to plan on getting a new one in the not too distant future or to wait a few more years before it might be an issue?

Thank you in advance,

Kat

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[Ian Mayes]

a typical copper or stainless steel hot water cylinder should last 30 years without too much bother. You do have to watch for glass lined steel ones though.

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[Fred Braxton]

I agree with you Ian, there’s no hard and fast rule. A copper HWC on a soft water supply should last at least 25 years and I met one that was 55 and still going! I recently replaced one that was 35 years old. Older cylinders seem to last longer too, as they appear to be made of thicker or higher-quality copper than modern ones. In hard-water areas, expect a shorter life.

If the water is hard, acidic, has sediment or is otherwise corrosive that will shorten the HWC’s life — copper, steel or stainless. Roof water is slightly acidic, though if it’s stored in a concrete tank that will offset the acidity somewhat.

Another important longevity factor is temperature: the hotter the water, the faster the corrosion. People sometimes set the thermostat well above the recommended 60C, perhaps to compensate for a cylinder that’s not big enough for the demand. Plumbers often install HWCs with the setting at 70 or above. An EDA or HPA would pick that up by measuring the temperature at a tap. Or at the pipework if there’s a tempering valve.

Traditional thermostats don’t make it any easier. They’re notoriously inaccurate: I saw one where the pointer said it was set at 60 but the temperature at the tap was 70. And it’s often difficult to read the setting.

A glass-lined steel HWC has a sacrificial anode. The anode corrodes first before the steel. Therefore the anode needs to be replaced every few years, but rarely does that happen, so bang goes the longevity.

Stainless is good provided the steel is of good quality——hard to guarantee these days.

Another factor is water hammer. If a tap gets turned off sharply, or a solenoid in a washing machine or dishwasher shuts too suddenly, it can cause a shock wave that travels through the pipework and vibrates everything. You get flexing of the cylinder walls and eventually a crack. This happened to our stainless solar cylinder that was only 13 years old.

Lastly, over-pressure will shorten the life of a HWC. Some city water is supplied at a much higher pressure than is good for HWCs etc. Low-pressure cylinders have a pressure-reducing “Ajax” valve or the like to protect them but these need replacing every 10 years or so.

Kat, your client could check out the above to get some indication of the expected life. Their neighbours may have some experience too.

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[Kat Achterberg]

Thank you Ian and Fred, this is certainly most helpful.

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