Hot Water System Valves and Fittings: What Do You Need?

Jun 29, 2026

Buying a hot water system is only part of the job. Most replacements also need the right valves, fittings, pipework connections, drainage parts and compliance components. The exact parts depend on the system type, water pressure, location, temperature control requirements and whether the replacement is electric, gas, instant gas or heat pump. At Hot Water Outlet, you can compare supply-only hot water systems online, including electric hot water systems, heat pump hot water systems, gas hot water systems, instant gas hot water systems and compatible valves, pipework and fittings.

Quick Answer

Most hot water system replacements may require more than the unit itself.

Common hot water system valves and fittings can include:

Tempering valve
Pressure limiting valve
Duo valve
Expansion control valve
Isolation valve
Non-return valve
Pressure and temperature relief valve
Cold water expansion valve
Relief drain pipework
Connection fittings
Pipework materials
Safe tray components
Condensate drainage parts for heat pumps
Gas isolation valve for gas systems
Controller or electrical accessories where applicable

The exact parts depend on the system, installation location and site conditions. A licensed plumber, gas fitter or electrician should confirm what is required.

Supply-only pricing for a hot water system usually does not include valves, fittings, pipework changes, installation, plumbing labour, electrical work, gas fitting, drainage work, old unit removal, disposal or compliance upgrades unless specifically shown at checkout.

Common Hot Water Valves and Fittings

Part	What It Does	Commonly Used With
Tempering valve	Blends hot and cold water to reduce outlet temperature	Storage systems, heat pumps, some gas systems
Pressure limiting valve	Reduces incoming water pressure to protect the system	Electric, gas, heat pump and storage systems
Duo valve	Combines isolation and non-return functions in some setups	Storage hot water systems
Expansion control valve	Helps manage expansion pressure on the cold water side	Storage systems in some installations
Isolation valve	Allows water or gas supply to be isolated	Most hot water systems
Non-return valve	Helps prevent reverse flow	Many hot water installations
Relief valve drain	Carries discharge safely away from the unit	Storage systems and heat pumps
Safe tray	Helps manage leaks or discharge in indoor locations	Indoor tanks and cupboard installs
Condensate drain	Drains normal heat pump condensate	Heat pump hot water systems
Gas isolation valve	Allows gas supply to be isolated	Gas and instant gas systems

Why Valves and Fittings Matter

Hot water valves and fittings are not just accessories. They help manage pressure, temperature, isolation, drainage and system protection.

They can affect:

Hot water safety
Temperature control
Water pressure
System warranty conditions
Compliance
Ease of servicing
Leak prevention
Drainage
Future replacement
System performance

Old valves may look reusable, but they may be seized, leaking, non-compliant, damaged, incorrectly sized or unsuitable for the new system.

Supply-Only Pricing and Valves

Hot Water Outlet sells supply-only hot water systems and accessories online. A supply-only hot water system price usually means the product price, not a complete installed job.

Supply-only pricing usually does not include:

Installation
Plumbing labour
Electrical work
Gas fitting
Old unit removal
Disposal
Valves
Fittings
Pipework changes
Drainage work
Switchboard upgrades
Electrical circuit upgrades
Gas upgrades
Regulator changes
LPG bottle work
Controller wiring
Compliance upgrades
Concrete bases or platforms
Delivery beyond what is shown at checkout

This is why it is important to compare both the hot water unit and the compatible valves, pipework and fittings that may be needed.

Tempering Valve

A tempering valve blends hot water from the hot water system with cold water to deliver water at a safer controlled temperature to sanitary fixtures.

Tempering valves are commonly used with:

Electric storage hot water systems
Heat pump hot water systems
Gas storage systems
Some replacement installations
Homes with bathroom outlets
Rental properties
Family homes

A tempering valve may be required depending on the system, temperature setting, outlet use and compliance requirements.

Tempering Valve Buyer Checks

Check:

Whether the system stores water above delivery temperature
Whether bathrooms are supplied
Existing valve age and condition
Whether the valve is leaking or seized
Connection size
Installation location
Local compliance requirements
Licensed plumber confirmation

Do not assume the old tempering valve can always be reused. If it is old, faulty or not suitable, replacement may be required.

Pressure Limiting Valve

A pressure limiting valve reduces incoming water pressure before it enters the hot water system.

High water pressure can affect valves, pipework and the hot water unit. A pressure limiting valve may be needed where the incoming mains pressure is higher than the system or plumbing setup allows.

Pressure limiting valves are commonly used with:

Electric hot water systems
Heat pump hot water systems
Gas hot water systems
Storage hot water systems
Some instant gas installations depending on site conditions

Pressure Limiting Valve Buyer Checks

Check:

Incoming water pressure
System maximum pressure rating
Existing valve condition
Whether the old valve is leaking
Whether pressure is too high
Whether water hammer is present
Correct pressure rating
Licensed plumber confirmation

A licensed plumber should confirm whether a pressure limiting valve is required and what rating is suitable.

Duo Valve

A duo valve is commonly used on some storage hot water installations and can combine isolation and non-return functions in one valve body.

A duo valve may be used with:

Electric storage systems
Heat pump systems
Gas storage systems
Replacement storage tanks

Duo Valve Buyer Checks

Check:

Whether the existing setup has a duo valve
Whether it is leaking
Whether it turns freely
Whether it suits the replacement system
Connection size
Direction of flow
Whether additional valves are required
Licensed plumber confirmation

Old duo valves may seize or leak and may need replacement during a hot water changeover.

Expansion Control Valve

An expansion control valve can help manage pressure caused by thermal expansion in a storage hot water system.

As water heats, it expands. Depending on the system, local requirements and pressure setup, expansion control may be needed on the cold water side.

Expansion control valves may be used with:

Electric storage systems
Heat pump hot water systems
Gas storage systems
Some high-pressure storage systems

Expansion Control Valve Buyer Checks

Check:

Whether the system requires one
Existing valve condition
Drainage point
Water pressure
Storage tank requirements
Local compliance requirements
Licensed plumber confirmation

Not every setup is the same. The correct valve arrangement should be confirmed for the specific system and property.

Pressure and Temperature Relief Valve

A pressure and temperature relief valve is an important safety valve on many storage hot water systems.

It is designed to discharge water if pressure or temperature conditions require relief. This discharge must be directed safely.

Pressure and temperature relief valves are commonly associated with:

Electric storage hot water systems
Heat pump hot water systems
Gas storage hot water systems
Storage tanks

Relief Valve Buyer Checks

Check:

Whether the valve is supplied with the system
Whether replacement is required
Drain line location
Safe discharge point
Signs of constant leaking
Signs of corrosion
Pipework condition
Licensed plumber confirmation

Do not block, cap or ignore relief valve discharge. Relief valves need safe drainage.

Isolation Valves

Isolation valves allow water, gas or other services to be turned off for servicing or replacement.

Hot water installations may include:

Cold water isolation valve
Gas isolation valve
Appliance isolation valve
Fixture isolation valve
Line isolation valve

Isolation valves make future servicing easier and safer.

Isolation Valve Buyer Checks

Check:

Whether isolation valves are already installed
Whether they turn off properly
Whether they leak
Whether they are accessible
Whether a gas isolation valve is required
Whether valves are correctly located
Licensed trade confirmation

A valve that exists but cannot be turned may not be useful during replacement or future servicing.

Non-Return Valve

A non-return valve helps prevent reverse flow in pipework.

Non-return valves may be built into certain valve assemblies or installed separately depending on the system design.

They may be relevant for:

Storage hot water systems
Pressure control setups
Cold water inlet arrangements
Some valve packs

Non-Return Valve Buyer Checks

Check:

Whether the existing setup includes one
Whether it is built into another valve
Direction of flow
Compatibility with the system
Local compliance requirements
Licensed plumber confirmation

The correct arrangement depends on the system and plumbing setup.

Relief Drain Pipework

Relief valve discharge must be drained safely.

Drainage may be needed for:

Pressure and temperature relief valve discharge
Expansion control valve discharge
Safe tray drainage
Heat pump condensate
Storage system discharge points

Poor drainage can cause:

Water damage
Staining
Slippery surfaces
Nuisance discharge
Compliance issues
Damage to walls, paths or foundations

Drainage Buyer Checks

Check:

Existing drain location
Whether discharge is visible
Whether discharge runs to a safe point
Whether the drain is blocked
Whether pipework needs replacement
Whether the new unit changes valve positions
Whether condensate drainage is needed
Licensed plumber confirmation

Drainage is often overlooked when buying a supply-only hot water system online.

Safe Tray and Drainage Parts

Indoor hot water systems may need a safe tray and drain depending on the location and setup.

A safe tray can help manage water from leaks or discharge where a hot water system is installed in a cupboard, ceiling space, internal room or other sensitive area.

Safe tray requirements may apply to:

Indoor electric storage systems
Indoor heat pump storage tanks where suitable
Cupboard installations
Apartments
Townhouses
Laundry installations
Systems above habitable areas

Safe Tray Buyer Checks

Check:

Indoor installation location
Existing tray size
Existing drain point
Whether the tray is damaged
Whether the new system fits the tray
Whether the tray drain is clear
Licensed plumber confirmation

A new tank may not fit an old tray if the diameter or base size is different.

Heat Pump Condensate Drainage

Heat pump hot water systems produce condensate during normal operation.

This condensate needs a safe drainage path.

Heat pump drainage checks include:

Condensate outlet location
Drain point location
Whether water will pool
Whether the area becomes slippery
Whether the drain is visible
Whether the condensate line can be run safely
Whether the system location allows drainage
Whether relief valve drainage is separate or combined where allowed

Heat pumps also need airflow, noise placement and electrical supply checks. Condensate drainage is only one part of the suitability check.

Gas Hot Water Fittings

Gas hot water systems and instant gas hot water systems need correct gas fittings and licensed gas fitting work.

Gas-related fittings may include:

Gas isolation valve
Gas connection fittings
Gas pipework
LPG regulator components
Appliance connection parts
Flue components for internal/flued units
Controller wiring accessories where applicable

Natural gas and LPG are not interchangeable. A natural gas unit must not be connected to LPG unless it is specifically converted and approved by a licensed gas fitter. An LPG unit must not be connected to natural gas unless the same applies.

External gas hot water units are outdoor/external only unless the product is specifically designed and approved for internal or flued installation.

Gas Fitting Buyer Checks

Check:

Natural gas or LPG
Gas pipe sizing
Gas meter capacity
LPG bottle setup
LPG regulator capacity
Appliance location
Clearances
Flue requirements
Gas isolation valve
Licensed gas fitter requirements

Gas fitting work must be completed by a licensed gas fitter.

Instant Gas Fittings and Accessories

Instant gas hot water systems may need extra parts beyond the unit.

These may include:

Cold water isolation valve
Gas isolation valve
Connection fittings
Controller wiring
Temperature controllers
Power point or electrical provision
Flue kit for approved internal/flued models
Pipework alterations
Pressure control valves where required

Common instant gas checks include:

16L, 20L or 26L flow rate
Natural gas or LPG
Water pressure
Minimum flow rate
Gas pipe sizing
Controller compatibility
External clearances
Flue requirements if internal

If replacing an old instant gas unit, do not assume the old controllers, fittings or pipe positions will match the new model.

Electric Hot Water Valves and Fittings

Electric hot water systems often need a standard set of plumbing valves and fittings.

These may include:

Tempering valve
Pressure limiting valve
Duo valve
Expansion control valve
Isolation valve
Non-return valve
Relief valve drain pipework
Connection fittings
Safe tray if indoors
Electrical isolation or circuit work by a licensed electrician

Electric Storage Buyer Checks

Check:

Tank size
Element rating
Indoor or outdoor rating
Existing valves
Drainage
Water pressure
Safe tray requirements
Electrical supply
Licensed plumbing and electrical requirements

A replacement electric tank may also need pipework changes if the new unit has different connection points.

Heat Pump Valves and Fittings

Heat pumps use stored hot water, so they often need many of the same valves as electric storage systems, plus condensate drainage.

Common heat pump-related parts may include:

Tempering valve
Pressure limiting valve
Duo valve
Expansion control valve
Isolation valve
Non-return valve
Relief drain pipework
Condensate drain materials
Connection fittings
Base or platform materials where required
Electrical connection by a licensed electrician

Heat Pump Buyer Checks

Check:

Outdoor airflow
Condensate drainage
Relief valve drainage
Noise placement
Electrical supply
Existing valve condition
Existing base or slab
Pipework connection locations
Access for servicing
Licensed trade requirements

Heat pump rebates, STCs and incentives can change and depend on product, installer, property, purchase type and program rules. Do not assume a rebate applies without checking current eligibility.

Valves for Replacing Gas With Electric

Changing from gas hot water to electric or heat pump may require different valves and fittings.

This may involve:

Gas isolation or capping by a licensed gas fitter
New water isolation valves
Tempering valve
Pressure limiting valve
Expansion control valve
Drainage pipework
Electrical circuit work
Pipework changes
Heat pump condensate drainage if applicable

Changing system type is not usually a direct product swap. The full plumbing, electrical and gas disconnection requirements should be checked before buying.

Valves for Replacing Solar Hot Water

Replacing solar hot water may involve extra fittings because the old system may include roof collectors, a ground tank, a roof tank, solar pipework, a pump, controller and booster.

Parts and work may include:

Solar pipework isolation
Tempering valve
Pressure limiting valve
Expansion control valve
Drainage pipework
Booster connection changes
Gas or electrical disconnection
Heat pump condensate drainage if replacing with heat pump
Roof collector removal parts where arranged separately

Supply-only pricing does not usually include roof collector removal, roof tank removal, crane work, roof repairs or solar pipework decommissioning.

Do You Need New Valves When Replacing a Hot Water System?

Often, yes.

New valves may be needed because:

Existing valves are old
Existing valves are leaking
Existing valves are seized
Existing valves are non-compliant
The new system has different requirements
Water pressure needs control
Temperature control is required
Drainage needs upgrading
Pipework layout changes
Warranty or installation conditions require suitable valve setup

A licensed plumber should confirm what can be reused and what needs replacing.

Can You Reuse Old Hot Water Valves?

Sometimes, but it depends on condition, compliance and suitability.

Old valves may not be suitable if they are:

Leaking
Corroded
Seized
Incorrectly rated
Installed in the wrong location
Not compliant
Missing key functions
Not compatible with the new system
Past reasonable service life
Showing signs of pressure or temperature issues

Reusing old valves may save money upfront, but it can create leaks, performance issues or compliance problems later.

What Fittings Are Needed for a Like-for-Like Replacement?

A like-for-like replacement may still need valves and fittings.

For example, replacing electric storage with electric storage may still require:

Tempering valve
Pressure limiting valve
Duo valve
Expansion control valve
Relief drain pipework
Connection fittings
Safe tray parts if indoors
Electrical isolation or reconnection

Replacing instant gas with instant gas may still require:

Gas isolation valve
Water isolation valve
Gas connection fittings
Controller wiring changes
Pipework alterations
Power point check
Flue or clearance checks

Like-for-like does not always mean no extra parts.

What Fittings Are Needed When Changing System Type?

Changing system type usually needs more parts and labour.

Examples include:

Electric storage to heat pump
Gas to heat pump
Gas to electric storage
Solar to heat pump
Gas storage to instant gas
Instant gas to electric storage

Extra requirements may include:

New pipework
New drainage
Condensate drain
New electrical circuit
Gas capping
Gas pipe upgrades
Controller removal
Safe tray changes
New base or slab
Additional valves
Compliance upgrades

Before changing system type, compare the full installed cost, not only the supply-only product price.

Common Mistakes With Hot Water Valves and Fittings

Assuming the Unit Comes With Everything

Some parts may be supplied with the unit, but many installation valves and fittings are separate.

Reusing Old Valves Without Checking

Old valves may be seized, leaking or unsuitable.

Forgetting the Tempering Valve

Temperature control may be required depending on the system and outlets.

Ignoring Water Pressure

High pressure can affect the system and valve setup.

Forgetting Drainage

Relief valve discharge and heat pump condensate need safe drainage.

Buying the Wrong Gas Type

Natural gas and LPG are not interchangeable.

Using External Gas Units Indoors

External gas hot water units are outdoor/external only unless approved for internal or flued installation.

Not Allowing for Heat Pump Condensate

Heat pumps produce condensate during normal operation.

Comparing Product Price Only

Supply-only pricing may not include valves, fittings, pipework changes, labour or compliance upgrades.

Not Using Licensed Trades

Plumbing, gas fitting and electrical work must be completed by appropriately licensed tradespeople.

Buyer Checklist Before Ordering Valves and Fittings

Before ordering hot water valves and fittings, confirm:

Hot water system type
Tank size or flow rate
Electric, gas, heat pump or instant gas setup
Natural gas or LPG if applicable
Indoor or outdoor location
Water pressure
Existing valve condition
Existing drainage
Safe tray requirements
Tempering valve requirements
Pressure limiting valve requirements
Expansion control requirements
Isolation valve requirements
Non-return valve requirements
Relief drain pipework
Heat pump condensate drainage if applicable
Gas isolation requirements if applicable
Pipework connection sizes
Licensed trade requirements
Whether parts are included with the unit or bought separately

FAQ: Hot Water System Valves and Fittings

What valves are needed for a hot water system?

Common valves may include a tempering valve, pressure limiting valve, duo valve, expansion control valve, isolation valve, non-return valve and relief valve setup. The exact valves depend on the system and property.

Do I need a tempering valve?

A tempering valve may be required depending on the system, storage temperature, outlet type and compliance requirements. A licensed plumber should confirm what applies.

What does a pressure limiting valve do?

A pressure limiting valve reduces incoming water pressure to help protect the hot water system and plumbing setup.

What does a duo valve do?

A duo valve can combine isolation and non-return functions in some storage hot water installations.

What is an expansion control valve?

An expansion control valve helps manage pressure caused by water expanding as it heats in a storage system.

Can I reuse my old hot water valves?

Sometimes, but only if they are suitable, compliant and in good condition. Old valves may be leaking, seized or unsuitable for the new system.

Do heat pumps need special fittings?

Heat pumps often need standard storage hot water valves plus condensate drainage. They also need suitable airflow, drainage, electrical supply and noise placement.

Do gas hot water systems need different fittings?

Gas systems may need gas isolation, gas connection fittings, correct gas pipework, flue components where applicable and licensed gas fitting. Natural gas and LPG are not interchangeable.

Are valves and fittings included in supply-only pricing?

Usually no. Supply-only pricing generally does not include valves, fittings, pipework changes, installation labour, electrical work, gas fitting or compliance upgrades unless specifically shown.

Can Hot Water Outlet install valves and fittings?

Hot Water Outlet sells supply-only hot water systems and accessories online. Plumbing, gas fitting and electrical work must be completed by appropriately licensed tradespeople. Where appropriate, Hot Water Outlet may help organise quotes from reputable installers.

Final Thoughts

Hot water systems often need more than just the unit. Valves, fittings, pipework connections, drainage, pressure control, temperature control and isolation all matter.

Before ordering online, check the system type, water pressure, drainage, location, gas type, electrical requirements and whether old valves can be reused. A licensed plumber, gas fitter or electrician should confirm what is required for the property.

Browse valves, pipework and fittings, compare hot water systems, electric hot water systems, heat pump hot water systems, gas hot water systems and instant gas hot water systems online at Hot Water Outlet.

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