What Is a Low Pressure Hot Water System?
A low pressure hot water system is a gravity-fed setup where water flows from a small header tank (sometimes called a cistern) in the ceiling down to the hot water cylinder below. The pressure at your hot taps is created entirely by gravity — the higher the header tank sits above the tap, the more pressure you get. In most Auckland homes, this gives around 1 to 2 metres of head pressure, which is significantly lower than mains pressure.
The header tank is fed by a ball valve connected to the mains supply. As hot water is used, cold water enters the header tank and flows down into the cylinder to be heated. This keeps the system topped up automatically, but the pressure remains limited by the height difference between the tank and the outlet.
Low pressure cylinders are typically copper and are commonly found in a hot water cupboard. They have a vent pipe running up through the ceiling rather than a TPR valve with a drain pipe like mains pressure systems.
Rheem low pressure electric cylinder installed by Water & Gas Worx
How to Identify a Low Pressure System
If you are not sure whether your home has a low pressure system, here are the telltale signs:
- Header tank in the ceiling — climb into the ceiling space and look for a small plastic or copper tank, usually near the hot water cylinder or above the bathroom. This is the single clearest indicator.
- Low flow from hot taps — if the hot water comes out noticeably weaker than the cold, you almost certainly have low pressure hot water.
- Hot and cold at different pressures — when you run a mixer tap or shower, the cold side is much stronger than the hot side. This pressure imbalance is characteristic of gravity-fed systems.
- Older style shower heads — many low pressure homes have been fitted with shower heads specifically designed to work with low flow, or have had pressure-limiting valves installed on the cold side to balance the two.
Common in Older Auckland Homes
Low pressure hot water systems were the standard installation in New Zealand homes built before the late 1980s and into the 1990s. They are especially common in Auckland suburbs with older housing stock, including Grey Lynn, Mt Eden, Ponsonby, Devonport, and Remuera. Many of these homes still have their original low pressure cylinder, or have had it replaced like-for-like over the years.
If your home was built before about 1990, there is a good chance it was plumbed for low pressure hot water. Even if the cylinder has been replaced, the pipework and header tank setup usually remain the same unless someone has done a full conversion.
Advantages of Low Pressure Systems
- Lower upfront cost — low pressure cylinders are cheaper to buy and install than mains pressure equivalents. The plumbing is simpler with no pressure-reducing valve, expansion vessel, or tempering valve required, which keeps the installation cost down.
- Compatible with older homes — if your home was plumbed for low pressure (pre-1990s), a like-for-like replacement is straightforward. No pipework upgrades, no new valves, no tapware changes. The existing infrastructure stays as-is.
- Simple and reliable — fewer components means fewer things to go wrong. There are no PRVs to fail, no expansion vessels to check, and no tempering valves to maintain. The system relies on gravity, which does not break down.
Disadvantages of Low Pressure Systems
- Low shower pressure — the most common complaint. Gravity-fed pressure often feels inadequate, especially with modern rain shower heads.
- Limited fixture compatibility — many modern mixer taps and thermostatic shower valves are designed for equal pressure systems and do not perform well on low pressure hot water
- Unbalanced hot and cold — the cold water runs at mains pressure while the hot runs at gravity pressure, which causes issues with mixing valves and some dishwashers or washing machines
- Header tank maintenance — the ball valve in the header tank can stick or fail, and the tank itself can deteriorate over time
Repair Services
We carry out all common repairs on low pressure hot water cylinders, including:
- Element replacement — the most frequent repair. When the element burns out, there is no hot water. We carry common element sizes on the van for same-day repairs in most cases.
- Thermostat replacement — if the water is overheating, not reaching temperature, or tripping the power, the thermostat may need replacing
- Pressure relief valve replacement — the pressure relief valve is a critical safety device. If it is dripping or stuck, it needs to be replaced immediately.
- Header tank ball valve — if the header tank is overflowing or not filling, the ball valve needs servicing or replacing
Upgrade Options
If you are tired of low water pressure in the shower or want to use modern fixtures, there are two main upgrade paths:
Convert to Mains Pressure
We can remove the header tank and replace your low pressure cylinder with a mains pressure cylinder. This gives you full street pressure at every hot tap. The existing pipework may need upgrading depending on its age and material, and we will need to install a pressure-reducing valve, expansion control valve, and tempering valve. It is a bigger job than a straight swap, but the improvement in water pressure is significant.
Switch to Continuous Flow
If you have gas to the property, a continuous flow gas hot water unit is another excellent upgrade option. It removes the cylinder entirely, frees up space, and delivers endless hot water at mains pressure. This is often the best option for homes where space is tight or hot water demand is high.
What's Included in a Low Pressure Cylinder Installation
Every low pressure cylinder replacement we do includes the core parts and labour needed to leave the job safe, compliant, and warranty-registered:
- Supply of new low pressure cylinder (Rheem, HJ Cooper or Dux)
- Disconnection and removal of the existing cylinder
- Supply and install low pressure valve pack
- Supply and install cylinder safe tray
- Electrical switch kit
- Connection to existing plumbing
- Warranty registered with manufacturer
Brands We Work With
For low pressure cylinder replacements, we supply and install units from Rheem, HJ Cooper, and Dux. These brands manufacture purpose-built low pressure cylinders in a range of sizes from 135 litres through to 300 litres. We will recommend the right size based on the number of people in your household and your hot water usage patterns.
If your existing cylinder is beyond repair and you want to replace it like-for-like, we can usually have a new one installed within a day. If you would prefer to upgrade to mains pressure or continuous flow at the same time, we will talk you through the options and give you a clear price before any work starts.
