What is a tempering valve?

A tempering valve is a safety device fitted to hot water systems in Queensland homes to control the temperature of hot water delivered to bathrooms and reduce the risk of scalding. This article explains what a tempering valve does, why it is required under Australian Standards, how long it lasts, and when it should be checked or replaced by a licensed plumber.

Why is a tempering valve important?

Hot water can cause serious burns and scalds very quickly, particularly for children and elderly occupants.

Water stored in a hot water system is required to be kept at 60°C, which can cause a third-degree burn in less than five seconds for an adult, and in around one second for a child.

A tempering valve significantly reduces this risk by limiting the temperature of hot water delivered to bathroom fixtures. When water is supplied at 50°C, the likelihood of serious scalding is greatly reduced. At approximately 49°C, it can take up to five minutes for a severe burn to occur.

What does a tempering valve do?

A tempering valve (also referred to as a mixing valve) works by blending hot and cold water to deliver water at a safe, consistent temperature.

A typical tempering valve consists of three connections:

• Hot water inlet

• Cold water inlet

• Outlet supplying mixed hot and cold water

Inside the valve is a thermostatic element that reacts to temperature changes by expanding and contracting. This adjusts the flow of hot and cold water to maintain a consistent outlet temperature, usually accurate to within ±3°C of the set temperature.

Why must hot water systems be set to at least 60°C?

Under the Plumbing Code of Australia (PCA) and Australian Standard AS3500.4.2, hot water systems must store water at a minimum temperature of 60°C.

This requirement exists to prevent the growth of Legionella bacteria, which can cause Legionnaires’ disease — a serious illness that can be harmful or fatal to humans.

Tempering valves allow systems to meet this safety requirement while still delivering water to bathrooms at a safer temperature.

Tempering valve temperature limits in Queensland

Queensland plumbing regulations specify maximum outlet temperatures:

• Bathrooms: Basins & Showers Hot water must not exceed 50°C

• Childcare centres, schools, hospitals, aged care and similar facilities: Hot water must not exceed 45°C

Kitchens and laundries are typically permitted to bypass the tempering valve.

Do all hot water systems require a tempering valve?

Most hot water systems with a storage tank require a tempering valve, including:

• Electric storage systems

• Gas storage systems

• Solar hot water systems

• Heat pump systems

Instantaneous (continuous flow) hot water systems do not generally require a tempering valve, as they regulate temperature internally. However, this depends on the system design and installation requirements.

Can a tempering valve be adjusted?

Hot water temperature supplied to bathrooms must not exceed 50°C.

If you would like the temperature set lower than this, the adjustment must be carried out by a licensed plumber. Homeowners are not permitted to adjust tempering valves themselves.

How long do tempering valves last?

Most manufacturers recommend replacing tempering valves approximately every five years, depending on water quality and maintenance.

Annual servicing by a licensed plumber typically includes:

• Removing internal scale build-up (a common cause of failure)

• Cleaning strainers and filters

• Flushing the system

This servicing can be carried out at the same time as routine hot water system maintenance and can help extend the lifespan of both the tempering valve and the hot water system.

How can you tell if a tempering valve is failing?

Some tempering valves include a thermal shut-off feature that closes the hot and cold inlets if a fault occurs. Whether this feature is present or not, common signs of a failing tempering valve include:

• Loss of hot water

• Lower than normal hot water temperature

• Reduced hot water pressure

• Inconsistent temperature at bathroom fixtures

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When to call a licensed plumber

You should contact a licensed plumber if:

• Hot water temperature is inconsistent

• Hot water is not reaching safe temperatures

• Water pressure has noticeably reduced

• You are unsure whether your system meets current safety requirements

• A tempering valve has not been serviced or replaced in several years

Tempering valves are a regulated safety device and must only be serviced, adjusted, or replaced by a licensed plumber.

Learn more about hot water system care

For a complete guide to maintaining hot water systems in Brisbane, including safety components like tempering valves, see our article on how to maintain a hot water system in Brisbane’s climate.

If you’re preparing for cooler weather, you may also find our guide on checking your hot water system before winter in Brisbane helpful.

Frequently asked questions about tempering valves

Is a tempering valve required in Queensland? Yes. Queensland plumbing regulations require tempering valves to limit hot water temperature to bathrooms to reduce the risk of scalding.

How often should a tempering valve be replaced?Most manufacturers recommend replacement every five years, depending on water quality and maintenance.

Can a tempering valve fail without warning?Yes. Scale build-up and internal wear can cause failure, which is why regular inspection is important.

Need a tempering valve checked?

If you believe your tempering valve may not be working correctly, or you’re unsure whether your hot water system meets current safety requirements, a licensed plumber can inspect the system and recommend the appropriate solution.

Howzat Plumbing services Brisbane and surrounding areas, including Chermside, the Northside, Southside, Moreton Bay, and surrounding suburbs.