Hot Water Cylinder Problems

The vast majority of hot water cylinders’ problems can be attributed to the quality of build and the technical specification of the components.

However, with an ever increasing focus on cost by some contractors, we are hearing more and more horror stories regarding problems caused by inferior quality cylinders – proving the old adage that you get what you pay for in life.

So in our continual quest for openness and promoting a full understanding of hot water solutions, here is our quick buyers’ guide to assessing the quality of a cylinder before you buy it.

Hot Water Cylinder Grade – Double Check the Thickness of Copper

There are 3 grades of Vented hot water cylinders covered by the British Standard BS1566 - namely Grade 1, Grade 2 and Grade 3. The grading is designed to provide guidance on the thickness of material to cope with different operating conditions as outlined below.


Thickness of Copper

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The variation in thickness within the grades will be dependent on the diameter of the cylinder and the incoming pressure. So a Grade 3, 450mm diameter vented cylinder would be made from 0.7mm thick copper. If the size increases to 500mm diameter we would expect to see 0.9mm thick materials and 600mm diameter would be manufactured from 1.2mm copper.

Sadly, we have heard growing reports of cylinders in the market place which are being passed off as higher grade cylinders but upon inspection are manufactured from thinner material. And in fact, we have seen cylinders manufactured to the now discredited Grade 4 specification, with thicknesses of as little as 0.55mm and badged as Grade 3 cylinders.

As you would expect, the thinner the material, the more likely the cylinder is to have problems such as leaks, splits and total failure.

TOP TIP: So before you place your order – don’t rely on the grade quoted by the manufacturer, double check the thickness of the material being used.

Performance of Coil Being Used in Hot Water Cylinders

The coil is one of the most important components in the hot water cylinder and therefore has a major impact on the overall performance of the cylinder, particularly reheat time, i.e., the time it takes for the cylinder to heat the contents to the specified temperature.

The issue with re-heat time as a measurement is that most manufacturers quote based on laboratory conditions using a large heat source, which may not be achieved in the general household.

The general method for assessing how much coil should be incorporated into a hot water cylinder has been down to surface area, generally measured in square metres. 

With the developments in coil technology, such as quick recovery finned copper coil, there is now a movement towards comparing coil performance on the kW rating.

TOP TIP: So before you order your cylinder, don’t simply rely on the quoted re-heat time, double check on the length of coil being used and the kW rating.

Hot Water Cylinder Insulation

The second performance indicator of a hot water cylinder is the heat loss rating, or to put it simply, the length of time it takes for the cylinder to cool down.  Obviously the lower the heat loss, the longer the water stays hot for and therefore the less energy required to re-heat the water.

The insulation on a hot water cylinder is the primary factor in determining the heat loss and therefore must be a key consideration in any buying decision.

Part L of the Building Regulations states that hot water cylinders for both new build and replacement cylinder will have a minimum of 50mm insulation.

PartL1B which covers the conservation of fuel and power in existing dwellings should have a minimum of 35mm insulation.

And whilst this is clear in its statement, the key aspect is total insulation of the cylinder so achieving 35 or 50mm insulation to the top, bottom and main body of the cylinder.

Unfortunately we have seen too many examples of cylinders where the insulation barely reaches the minimum insulation requirements to the main body and even less to the top and the bottom of the cylinder.

TOP TIP: So before you order your hot water cylinder, check the minimum insulation level.

Need More Help? 

If you would like more help to ensure you are receiving the optimum cylinder, contact our technical sales team on 01592 611123 or email us on