45°C and G12: Thermostatic or Pressure Balance for NZ Showers
For most homeowners a pressure balance valve gives simple anti scald protection at a lower cost, and it suits a straightforward single head shower. Choose a thermostatic valve when precise temperature control matters, when children or older adults use the shower, or when the system feeds multiple outlets. Building code and a licensed installer decide the final specification either way.
TL;DR:
Pressure balance valves are suitable for single-head showers with stable, well-balanced household pressure, offering lower cost and simpler installation.
Thermostatic valves provide more accurate temperature control and safety features, such as shutting off flow during cold water failure, making them ideal for at-risk users and multi-outlet systems.
It’s essential to check your household water pressure and pressure balance or thermostatic valve minimum requirements before selecting, especially if pressure is low or unbalanced.
Proper installation and commissioning by a licensed plumber are critical to ensure compliance with building codes and reliable operation of either valve type.
For reliable performance, a household static and running water pressure check during renovation is highly recommended, particularly in challenging pressure conditions.
Table of Contents
How pressure balance valves work
A pressure balance valve senses the incoming pressure of both the hot and cold supply lines and adjusts a single internal piston or disc to keep the ratio between them steady. If someone flushes a toilet or runs a tap elsewhere in the house, the valve compensates by shifting the mix so the ratio, and therefore the temperature, stays close to where it was set. It does not measure actual water temperature, only pressure, so a change in incoming hot water temperature itself (say the cylinder thermostat drifting) will still pass through to the shower.
This makes pressure balance valves a practical, lower cost choice for single head showers on a well balanced plumbing system. They react quickly to pressure fluctuations but offer less protection against a genuine temperature shift at the source.
Strength: Simple mechanism, fewer parts, generally cheaper to buy and install.
Limitation: Cannot correct for a hot water supply that is itself too hot or too cold.
Best fit: Single outlet showers where household pressure is stable and reasonably balanced.
How thermostatic valves control water temperature
A thermostatic valve, often called a TMV or thermostatic mixer, uses a heat sensitive element (typically a wax or bimetallic thermostat) to measure the actual mixed water temperature and adjust the hot and cold inflow to hold it steady. Unlike a pressure balance valve, it responds to temperature itself, not just pressure, so it corrects for both pressure changes and shifts in the incoming hot water supply. Most designs separate the temperature control from the flow control, letting you set a target temperature once and then adjust flow volume without disturbing it.
A key safety feature is shutdown behaviour: many thermostatic mixer showers reduce flow sharply or shut off almost completely if the cold supply fails, which limits scald risk for children and older people. This is one reason thermostatic valves are specified in households with at risk users and in showers feeding multiple heads or a handheld plus overhead combination.
Strength: Reacts to actual temperature, holds a set point tightly, and can shut down on cold failure.
Trade-off: Costs more, generally needs a higher minimum pressure, and has more parts to service.
Pro Tip: Ask your plumber for the valve’s minimum operating pressure before you buy. A thermostatic valve that needs more pressure than your home delivers will underperform no matter how good the brand.
Key differences and what they mean for your shower
The two valve types solve a similar problem in different ways, and the gap between them shows up most clearly under real household conditions rather than on a showroom wall.
Temperature accuracy: Thermostatic valves hold a set temperature more tightly because they measure it directly; pressure balance valves hold a ratio, which can drift if the hot water source itself changes temperature.
Cold water failure: Thermostatic valves typically reduce or stop flow if cold supply drops out; pressure balance valves maintain the pressure ratio but cannot detect a temperature only fault.
Multi outlet or low pressure systems: Thermostatic valves generally suit multiple simultaneous outlets and at risk users better, though some pressure balance and specialist mixers are built for low or unequal pressure situations, with some New Zealand products rated to operate down to very low pressures typical of challenging supply conditions.
Cost and commissioning: Pressure balance valves are usually cheaper and quicker to install; thermostatic valves cost more upfront and need careful commissioning to hit the correct delivery temperature.
Neither type is universally better. The right choice depends on your household, your pressure, and what the shower needs to do.
How to choose: a decision checklist for your renovation
Work through these steps before you commit to a valve type, ideally with your plumber alongside you.
Check your water pressure against the manufacturer’s minimum for any valve you are considering, since low or unbalanced pressure rules some options out.
Identify who uses the shower, because children, older adults or anyone with reduced sensation to heat are strong reasons to favour a thermostatic valve.
Count the outlets, since a shower with a rain head, handheld and body jets running together puts more demand on the valve than a single head.
Set your budget, weighing the lower upfront cost of pressure balance against the tighter control and safety shutdown of thermostatic.
Ask your plumber about minimum pressure requirements, how the valve will be commissioned, how accessible it will be for future servicing, and what warranty applies.
A red flag worth acting on: if your home has genuinely low or unequal pressure, or if anyone in the household is at higher risk of scalding, that points toward a thermostatic valve or an added tempering valve rather than a standard pressure balance unit.
Pro Tip: Get your household’s static and running water pressure measured during any bathroom renovation, not just when a fault appears. It is the single most useful number for choosing between valve types.
Installation and compliance: what the building code requires
Building Code Clause G12 sets maximum hot water delivery temperatures to prevent scalding, and the acceptable devices differ depending on the setting. Tempering valves are intended for delivery up to 50°C in general residential use, while thermostatic mixing valves are specified where a maximum of 45°C is required, such as for at risk users. The acceptable solutions and verification methods document for G12 references the AS 4032 series of standards for thermostatic mixing valves and tempering valves and sets out commissioning requirements.
Devices accepted under G12 include thermostatic mixing valves, thermostatically controlled taps, tempering valves and temperature limited water heaters, each matched to a specific delivery temperature limit.
Commissioning matters as much as device choice: a valve fitted but not correctly set to manufacturer pressure specifications will not deliver compliant temperatures.
Installation is a licensed plumber’s job, both for legal compliance and because correct isolation and testing at commissioning catches faults before they reach the shower.
Your renovation’s bathroom plumbing layout also affects which valve type is practical, particularly where pipe runs are long or multiple outlets share a supply.
Maintenance, common faults and expected lifespan
Both valve types wear over time, most often through cartridge wear, limescale build up, or a blocked inlet strainer restricting flow to one side. Thermostatic valves can also develop “hunting,” a temperature oscillation that signals a failing thermostatic element or a pressure imbalance beyond what the valve can correct.
Watch for slow leaks around the valve body, a noticeable drop in flow, or temperature that shifts when someone else in the house runs water. Most manufacturers recommend periodic servicing, and keeping the valve accessible behind an access panel, a point worth confirming during bathroom waterproofing and pre tile checks, makes future servicing far easier and keeps warranty terms intact.
Cartridge wear is the most common fault across both valve types and is usually a straightforward part replacement.
Hunting or temperature drift in a thermostatic valve often points to a pressure mismatch rather than a faulty unit.
Blocked strainers from sediment are a frequent, easily fixed cause of reduced flow on either valve type.
An installer’s view on valve choice in renovations
In practice, the valve type matters less than getting the pressures right and commissioning it properly. Sorted Home Solutions coordinates all trades on a renovation, plumbing included, so the valve is specified against your actual household pressures rather than a generic spec sheet. We see thermostatic valves earn their cost in multi outlet showers and homes with at risk users, and a quality pressure balance valve perform perfectly well everywhere else. Licensed installation and correct commissioning decide the outcome far more than the badge on the valve.
— Rudi
Get a pressure check or bathroom quote from Sorted Home Solutions
A shower valve is only as good as the plumbing behind it, and that is where a fixed-fee renovation avoids the guessing that comes with piecing a bathroom together trade by trade. Sorted Home Solutions manages licensed plumbing, tiling, waterproofing and fixtures as one coordinated job, with a single point of contact from first measure to final commissioning.
Fixed-fee bathroom packages cover a range of services from simple valve upgrades to full rebuilds.
Smaller jobs, including vanity and fixture swaps, suit homeowners who just need a valve replaced without a full renovation.
Full project coordination means your plumber, tiler and painter are scheduled together rather than left to chase each other.
Check current pricing or look through our bathroom renovation work to book a consult and get your home’s pressures and valve options assessed properly.
Official guidance and standards to consult
For the legal detail behind delivery temperature limits, read Clause G12 on preventing scalding and the underlying acceptable solutions document, which cites the AS 4032 standards for TMVs and tempering valves. For a construction quality perspective relevant to any plumbing installation, this building defects checklist is a useful reference for spotting issues before they affect a new valve.
Sources
FAQ
What is better, thermostatic or pressure balanced?
Neither is better in every case: thermostatic valves give tighter temperature control and shut down on cold water failure, making them the stronger choice for at risk users or multi outlet showers. Pressure balance valves cost less and suit straightforward single head showers on a stable, balanced supply.
What is the disadvantage of a thermostatic shower?
Thermostatic valves cost more to buy and install than pressure balance valves and generally need a higher minimum operating pressure to perform properly. They also have more internal parts, which means more that can eventually wear and need servicing.
What is the purpose of a thermostatic balancing valve?
A thermostatic mixing valve measures the actual mixed water temperature and adjusts hot and cold flow to hold that temperature steady, correcting for both pressure changes and shifts in the hot water source itself. Under Building Code G12, it is specified where a maximum delivery temperature of 45°C is required, such as for at risk users.
Is a thermostatic shower worth it?
It is worth it where children, older adults or anyone sensitive to sudden temperature change use the shower, or where the system feeds multiple outlets at once. For a simple, well balanced single head shower on stable pressure, a quality pressure balance valve often delivers the same everyday comfort for less money.
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