13 Apr 2024

Hot water cylinders explained – how they work

In New Zealand the most common form of hot water heating system is the humble hot water cylinder, low installation costs and proven reliability have made a firm favourite across the country for many many years. Although electricity is historically the most popular, these days hot water cylinders can be powered by gas, solar energy, heat pumps and wetback systems or mixed combinations of these methods.

How Do Hot Water Cylinders Work?

Simplicity has always been the key to the success of hot water cylinders, they deliver hot water right where you need it with a minimum of fuss. Similar to an electric jug, hot water cylinders rely on an element encased within an insulated and reinforced storage tank to heat and maintain the surrounding water to the required temperature, which is regulated by the cylinders thermostat. (In New Zealand the recommended hot water temperature is 60 degrees in the cylinder and no more than 55 degrees at the tap).

Essentially cold water automatically enters the cylinders storage tank when hot water exits, resulting in a lowering of the water temperature in the bottom of the tank, this then triggers the thermostat which allows the element to activate and heat the water to the set temperature again. This process continues 24/7 keeping you in a constant supply of perfectly heated hot water.

What Are The Components Of A Hot Water Cylinder?

  • The Storage Tank. Modern mains pressure hot water storage tanks will usually have a steel inner cylinder which is lined with glass or vitreous enamel, insulation and a steel outer lining. Depending on their age low pressure tanks may have a copper lining.
  • The Thermostat. Essentially a thermometer, the thermostat controls the water temperature inside the storage tank. The thermostat is fully automatic meaning power is only used when heating is required.
  • The Element. One and in some cases two immersion elements are located inside the storage tank, it creates the heat needed to heat the water. Some tanks will have two heating elements, each controlled by its own thermostat, only turning on when the water goes beneath the pre-set temperature.
  • The Temperature Pressure Relief Valve. This is there to protect the hot water cylinder from excess pressures and temperatures and hopefully avoid major damage to the cylinder and/or your house!
  • The Anode Rod. Wherever there is water there is going to be corrosion. In order to prolong the lifespan of the storage tank and reduce corrosion over time an anode rod is suspended within the tank to act as a sacrificial piece of metal. The Anode Rod is usually made of magnesium or aluminium with a steel core.
  • The Drain Valve. Used to drain the hot water cylinder of its water in order to make repairs, move or replace etc.


Need help deciding which hot water cylinder is right for you? Pete and the team are happy to help! Whether it is mains pressure hot water cylinders, low pressure hot water cylinders, gas hot water heating, an outdoor cylinder, solar, wetback powered hot water cylinders or the increasingly popular hot water heat pump system, the nationwide network of installers at The Cylinder Guy will provide you with the best match for your home or business. 


Contact the team today for a free assessment or learn more about our different hot water solutions.


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