Mains Pressure Hot Water Cylinder Supply & Installation

Main pressure hot water cylinder have become far more popular than low-pressure hot water cylinders in recent years, the main selling point is that they provide high pressure hot water at your home, are more reliable, modern and perform better than their low pressure counterparts.

hot water cylinder

What’s included in our service?

The team at Sumich Plumbing oversees your entire 

Our service includes:

  • Supplying the most appropriate mains pressure hot water cylinder for your property from brands such as Rinnai
  • Installing & configuring the mains pressure hot water cylinder.

Reliability and safety are also key aspects, one of the most common main pressure hot water cylinders in New Zealand is the Rinnai Hot Water Cylinder which come with a 20 year warranty.

Why invest into a mains pressure hot water system?


  • Hot water cylinders are very simple systems, which makes them a great hot water solution.
  • Similar to an electric jug, electric hot water cylinders make use of an element inside the storage tank to heat and maintain the water to 60 degrees.

Large Storage

  • Most modern hot water cylinders are mains pressure and have a capacity of 180 litres or bigger.


  • Mains pressure hot water cylinders can be electric or gas heated. Most homes in New Zealand have an electric hot water cylinder, older cylinders tend to be smaller and low pressure.

Mains Hot Water Cylinder Installation

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Why Choose Mains Hot Water Pressure In New Zealand?

Main pressure hot water systems provide a swift distribution of high pressured hot water across multiple faucets and showers without experiencing any reduction in pressure, whilst low pressure systems may lead to uneven pressure. So rest assured, you won’t have to wait for hot water to come out of your taps.

Advantages of Mains Hot Water Cylinders

  • Equal pressure of supplied hot and cold water
  • High-pressure hot water
  • Quick hot water delivery
  • Smaller diameter pipework can be used
  • The system allows for greater flexibility of pipe layout

Disadvantages of Mains Hot Water Cylinders

  • It can be noisy and subject to water hammer
  • There can be more water wastage
  • More valves are required in the system
  • There is increased wear and tear on the pipes and fittings
  • It can be difficult to install a wetback alongside this system

Key features of a mains hot water cylinder system

The thermostat acts as a thermometer and controls the water temperature inside the water storage tank. Power or gas  is only used when heating is required, meaning the thermostat is fully automatic.

In electric hot water cylinders one, sometimes two, immersion elements are located within the storage tank, these create the heat required to heat the water. In gas systems, the burner is located at the bottom of the cylinder with a flue running through the centre of the tank to exhaust toxic emissions.

Some tanks have two elements controlled by separate thermostats, only heating the water when the water temperature goes below a predetermined temperature. The temperature-pressure relief valve exists to protect the hot water cylinder from excess pressures and temperatures, avoiding major damage to the cylinder or your home. The anode rod protects the cylinder from corrosion. The anode rod is suspended in the tank to reduce corrosion over time and prolong the lifespan of the cylinder. The drain valve is used to drain water out if the cylinder should repairs be required. 

Cold water will enter the cylinder storage tank when hot water exits, this way the water temperature in the bottom of the cylinder storage tank is colder than the water at the top.

This triggers the thermostat, allows the element to activate and heat the temperature to the set temperature again. This process repeats 24/7 to ensure hot water is always available. Gas hot water cylinder work in a very similar way, the only difference being they burn gas to heat water at the bottom of the tank and do not have an element in the water. 

Mains pressure, open vented, storage water heater supply systems supply mains pressure hot water to all outlets; hot and cold water is delivered to outlets at the same pressure. These systems have an internal or external expansion vessel that allows the heated water to expand, the system must also include a pressure relief valve in the event the expansion vessel fails.

All mains pressure hot water cylinders (>120 kPa) require this pressure relief valve to be both temperature and pressure operated. If a mains pressure unvented system is used, valves must be specified for the particular system to achieve the required pressure rating. The problem with only having a single valve for relieving pressure is that hot water is wasted as the hot water expands during the frequent heat-up cycles.

To minimise wasting hot water, an expansion control valve, set at slightly less pressure, is installed on the inlet side of the cylinder and will relieve cold water during the heat up-cycle. The expansion control valve can normally drip up to 5 litres of water per day. Both valves must have the appropriately-sizes copper drain line that discharges to a safe and visible location. 

Frequently Asked Questions

The components of a mains pressure hot water cylinder are the storage tank, thermostat, element (electric system) or the burner (in the case of gas systems), temperature relief valve, anode rod and drain valve.

The storage tank will usually have an inner steel cylinder which is lined with glass or vitreous enamel, insulation and a steel outer lining. Vitreous enamel is a thin layer of glass fused to the surface of the metal at a very high temperature.

This high pressure hot water cylinder is becoming much more popular in New Zealand because of its seamless ability to provide hot water to a large household, without any disruptions.

Older electric hot water cylinders are often poorly insulated, which will lead to heat loss. It is worth wrapping the cylinder with insulation if the electric hot water system is less than “A” grade.

Gas hot water storage systems have a faster heat recovery time than a comparable electric hot water cylinder. Gas cylinders need to be installed in a well-ventilated area and flued to remove exhaust gases. This leads to long pipe runs and means that gas hot cylinder have higher heat losses than electric hot water cylinders. It is also not safe to wrap a gas hot water cylinder. 

For an in depth analysis of which hot water cylinder is better, please read our article here.

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