Made to measure

Hot water cylinders, copper or stainless steel, have been brought to my attention for failing in a short time. One report had many on the same housing estate that failed very quickly.

Here we look at the probable causes and solutions.

Make the grade

Cylinders made from copper or stainless steel have to be made to meet British Standards, that being, BS I566:2002 (Part L). Copper cylinders used to include a sacrificial anode that attracted corrosion to protect the tank, but they are now frequently no longer included in standard domestic sized cylinders. Copper cylinders come in three variants of grade. Grade 1 has the thickest copper sheet (from 1.2- 2.0mm) and is recommended for a head of pressure at 25 M. Grade 2 at 15 M (0.9- 1.4mm) and grade 3 at 10 M and have a thickness of material from (0.7-1.2mm) thick. The less head of pressure, the thinner the copper. However, what is also quoted is the pH value of the water.

Now, 7 on the pH scale is neutral which means if you have an area with high acidity (a lower pH value), then the grade 3 cylinder might not be the correct choice. Another factor of choice might be cost. If you buy the cheapest it’s cheap for a reason. A grade 1 cylinder is around three times the thickness as a grade 3 but is bound to last far longer.

The solution? Open vented cylinders can be found in stainless steel. These products will still have a limit on the pH value of the water within, as no manufacturer will guarantee a product against corrosion from water acidity or alkalinity. However, a stainless-steel cylinder is made of a much stronger material and resistance to corrosion ought to be greater.


Water dissolves some materials when in contact with them. The level of solvency-acidity, or limescale -Alkaline, depends upon:

1. The source of the water and natural geological conditions

2. The pH value of the water can also be affected by acid rain

The European directive for water quality warns:

The water quality shall be in accordance with European Council Directive 98/83 EC, or revised version at the date of installation, and is not fed with water from a private supply. Particular: Chloride content: Max. 200 mg/l Sulphate content: Max. 200 mg/l Combination chloride/sulphate: Max. 300 mg/l (in total).

Here in the UK, you will find varying degrees of water hardness. This is measured by the pH value – a numerical scale of acidity from 0-14 - which tells how acidic or alkaline the water is. More acidic water has a lower pH value and is corrosive, while more alkalinity the water is, the higher the pH value on the scale.

Members have raised concerns with pin holes in copper cylinders after just a few years. The worries are about the quality of the products, manufacturers warranties, their customers disappointment, the embarrassment to the original installer and the on-cost of replacement.

Buyer beware

Knowing the impact of water solvency and manufacturers’ Terms and Conditions on products is vital. A leaking cylinder due to corrosion might be perceived as the installer’s fault if the checks are not carried out at survey.

A new cylinder, either copper or stainless steel, has warranty. But if you step outside the terms and conditions you may be unable to argue for a replacement if there’s a fault.

Let us look at some terms and conditions – and their fixes:

1. Failure to carry out safety checks invalidates the warranty on an UVHW cylinder.

2. A lifetime guarantee will require registering via the manufacturer within 28 days of installation and proven servicing records along with the Benchmark document will be required. Is the customer aware of a guarantee? If the house is a new build, who goes back to service?

3. Things like immersion heaters, water control valves etc can have a two-year warranty when installed on a new build. If it’s a replacement retro fit, it’s one year.

4. Benchmark documents and proof of purchase should be with a consumer. Servicing records should also be with the consumer if it has been serviced.

5. The pH value of the water supply must be at 7.5. Can you prove this?

6. Exclusions are things like any labour charges for replacements, lime scale build up, or consequential losses occurred.

7. Water supplied from a main supply only. Not suitable from a private supply?

There are some variations of warranties, but they do focus on servicing, water quality and documentation. If any of this is not done, then it’s down to the installer and the consumer.

Of course, it’s not just the cylinder to consider. The copper pipes and terminal fittings will also be affected by the solvency of water.


Water can be treated with a water softener. It adds sodium so you must have a non-treated supply to at least the main drinking tap, normally the kitchen sink. This addition, when set and used correctly, will alter the pH value of the water and protect the system. In addition, the components, such as a cylinder will comply to their warranty specification.

So: checking the pH value before you start will save time, money and call back. And always read the T&Cs.

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