Pressure Relief Valve for Hot Water Systems: Complete Buyer’s Guide

Jun 29, 2026

A pressure relief valve is one of the key safety parts used on many hot water systems. It helps discharge water when pressure or temperature conditions need to be relieved, protecting the system and surrounding pipework. If you are replacing a hot water system, the pressure relief valve, drain line and related fittings should be checked before installation. At Hot Water Outlet, you can compare supply-only hot water systems and compatible valves, pipework and fittings, including options for electric hot water systems, heat pump hot water systems, gas hot water systems and instant gas hot water systems.

Quick Answer

A pressure relief valve helps relieve excess pressure from a hot water system by discharging water through a safe drain line.

Many storage hot water systems use a pressure and temperature relief valve, often called a PTR valve or TPR valve. Some systems may also use an expansion control valve on the cold water side.

Pressure relief valves may be relevant for:

Electric storage hot water systems
Heat pump hot water systems
Gas storage hot water systems
Solar hot water systems
Storage tanks
Some replacement hot water installations

The exact valve required depends on the system type, pressure rating, temperature rating, water pressure, drainage and compliance requirements.

A licensed plumber should confirm the correct valve type, rating and drainage setup.

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

Pressure Relief Valve Buyer Checklist

Check	Why It Matters
System type	Storage, heat pump, gas and solar systems may have different valve requirements
Valve rating	The valve must suit the hot water system
Water pressure	High pressure can affect valve operation
Drain line	Discharge must be directed safely
Existing valve condition	Old valves may leak, seize or fail
Existing drainage	Poor drainage can cause damage or nuisance discharge
Expansion control	Some systems may also need cold water expansion control
Pipe size	Connections must suit the installation
Location	The valve must be accessible for service and testing
Licensed plumber	Valve selection and installation should be confirmed by a licensed plumber

What Is a Pressure Relief Valve?

A pressure relief valve is a safety valve designed to discharge water when pressure needs to be relieved from the hot water system.

On many storage systems, the valve is a pressure and temperature relief valve. This means it can respond to pressure and temperature conditions.

The discharge from the valve must be directed to a safe location through suitable drain pipework.

A pressure relief valve should never be capped, blocked or ignored.

Pressure Relief Valve vs PTR Valve vs TPR Valve

You may see different names used for similar hot water safety valves.

Term	Meaning
Pressure relief valve	General term for a valve that relieves pressure
PTR valve	Pressure and temperature relief valve
TPR valve	Temperature and pressure relief valve
Relief valve	Shortened term often used for pressure or temperature relief valves
Expansion control valve	Valve that helps manage cold water expansion pressure on some systems

In domestic hot water, many people say “pressure relief valve” when they mean the pressure and temperature relief valve on the storage tank.

A licensed plumber should confirm the exact valve type needed for the system.

Why Pressure Relief Valves Matter

Pressure relief valves matter because hot water systems heat water in a closed or semi-closed system. As water heats, pressure can increase.

A correctly selected and installed valve helps:

Relieve pressure
Protect the storage tank
Protect pipework
Manage safety discharge
Support compliance
Reduce risk of uncontrolled pressure build-up
Allow maintenance and testing
Provide visible signs of valve discharge

A leaking, blocked or incorrect relief valve can create safety, performance and compliance problems.

Hot Water Systems That Commonly Use Pressure Relief Valves

Electric Storage Hot Water Systems

Electric hot water systems commonly use storage tanks, so pressure relief valve checks are important.

When replacing electric storage, check:

Existing pressure relief valve
Valve rating
Relief drain line
Safe discharge point
Water pressure
Pressure limiting valve
Expansion control valve requirements
Tank size
Indoor or outdoor location
Existing pipework condition

An old pressure relief valve may not be suitable for the replacement system, even if it appears to be working.

Heat Pump Hot Water Systems

Heat pump hot water systems also store hot water, so they usually need pressure relief and drainage checks.

Heat pumps may also need condensate drainage, which is separate from relief valve discharge.

When replacing or buying a heat pump, check:

Pressure relief valve requirements
Valve rating
Relief drain location
Condensate drain location
Existing drainage
Water pressure
Pressure limiting valve requirements
Expansion control valve requirements
Outdoor location
Access for servicing

Heat pumps also need airflow, noise placement and electrical supply checks. The relief valve is only one part of the complete installation setup.

Gas Storage Hot Water Systems

Gas hot water systems that store water also need correct pressure relief and drainage.

When replacing gas storage, check:

Natural gas or LPG
Existing valve setup
Valve rating
Relief drain pipework
Safe discharge point
Gas appliance location
Water pressure
Tank size
Flue or ventilation requirements if applicable
Required valve and fitting upgrades

Natural gas and LPG are not interchangeable. Gas fitting work must be completed by a licensed gas fitter.

Solar Hot Water Systems

Solar hot water systems can involve storage tanks, roof collectors, boosters and pipework. Pressure relief and safe discharge are important.

When replacing or modifying solar hot water, check:

Tank pressure relief valve
Collector relief requirements where applicable
Drainage
Booster type
Existing valve condition
Solar pipework
Roof-mounted components
Safe discharge locations
Whether the system is being changed to heat pump, electric or gas

Solar replacements can involve extra work, including solar pipework isolation, collector removal, roof tank removal, booster changes and crane or lifting requirements.

Instant Gas Hot Water Systems

Instant gas hot water systems do not store hot water in the same way as storage tanks, so their valve requirements can differ.

Instant gas systems may still need:

Isolation valves
Gas isolation valve
Pressure control valves where required
Drainage or relief arrangements where specified
Connection fittings
Controller wiring or electrical provisions
Licensed gas fitting

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

Where Is a Pressure Relief Valve Installed?

On many storage hot water systems, the pressure and temperature relief valve is installed directly into the hot water storage tank.

The discharge pipe then runs from the valve to a safe discharge point.

The exact location depends on:

System design
Manufacturer requirements
Tank connection points
Indoor or outdoor location
Safe tray setup
Drainage route
Access for servicing
Local compliance requirements

The valve must remain accessible. It should not be hidden where it cannot be inspected or serviced.

Where Should Relief Valve Water Drain?

Relief valve discharge must be directed safely.

A safe discharge point should be planned so water does not:

Damage walls
Damage floors
Damage foundations
Discharge onto electrical equipment
Create a slip hazard
Pool around the tank
Discharge into an unsafe location
Cause nuisance water problems
Damage landscaping or paths

Drainage requirements depend on the property and installation location. A licensed plumber should confirm the correct discharge setup.

Why Is My Hot Water Relief Valve Dripping?

Some discharge from a relief valve may occur during normal heating, especially where water expands as it heats. However, constant dripping or heavy discharge may indicate a problem.

Possible causes include:

High incoming water pressure
Faulty relief valve
Worn valve seat
Debris in the valve
Expansion pressure
Missing or faulty expansion control valve
Faulty pressure limiting valve
Overheating
Incorrect valve rating
System fault

Do not assume the relief valve is the only issue. A licensed plumber should check the full pressure and valve setup.

Signs a Pressure Relief Valve May Need Attention

A pressure relief valve may need checking if you notice:

Constant dripping
Heavy discharge
Water pooling near the system
Corrosion around the valve
A valve that has not been serviced or checked
Discharge pipe damage
Steam or very hot discharge
No visible discharge pipe
Water stains
Leaks around the valve body
Poor hot water system performance
Pressure issues

These signs do not always mean the valve itself is faulty, but they do mean the system should be checked.

Can a Pressure Relief Valve Be Reused?

Sometimes, but it depends on the valve condition, age, rating and suitability.

An old pressure relief valve may not be suitable if it is:

Leaking
Corroded
Seized
Incorrectly rated
Blocked
Not accessible
Missing a proper drain line
Not compatible with the replacement system
Showing signs of age or wear
Not compliant with the replacement setup

When replacing a hot water system, the valve setup should be checked rather than automatically reused.

Is a Pressure Relief Valve Included With a Hot Water System?

Sometimes, but not always in the way buyers expect.

Some hot water systems may include a pressure and temperature relief valve. Other valves, fittings, drain lines and installation parts may still be separate.

Before ordering, check:

Product inclusions
Whether the relief valve is supplied
Whether extra valves are required
Whether a pressure limiting valve is needed
Whether an expansion control valve is needed
Whether drain materials are included
Whether your plumber is supplying parts
Whether a full valve kit is separate

You can compare compatible valves, pipework and fittings online.

Pressure Relief Valve vs Expansion Control Valve

A pressure relief valve and an expansion control valve are not the same thing.

Valve	Main Job
Pressure and temperature relief valve	Relieves pressure or temperature conditions from the storage tank
Expansion control valve	Helps manage pressure from thermal expansion on the cold water side
Pressure limiting valve	Reduces incoming water pressure
Tempering valve	Controls delivered hot water temperature by mixing hot and cold water
Duo valve	Combines isolation and non-return functions in some setups

Some systems may need more than one valve. A pressure relief valve does not replace a tempering valve, pressure limiting valve or expansion control valve.

Pressure Relief Valve and Water Pressure

Water pressure is one of the biggest factors in hot water valve performance.

High incoming pressure can cause:

Relief valve discharge
Valve wear
Pipework stress
Water hammer
Leaks
Shortened component life

A pressure limiting valve may be needed to reduce incoming water pressure before it reaches the system.

A licensed plumber should check the pressure before deciding whether the pressure relief valve is faulty.

Pressure Relief Valve and Temperature

A pressure and temperature relief valve can respond to temperature conditions as well as pressure conditions.

If water temperature becomes too high, the valve may discharge.

Possible causes of temperature-related discharge include:

Thermostat issue
Overheating
Incorrect system setting
Faulty control component
Solar overheating
Incorrect valve rating
System fault

Very hot discharge should be treated seriously and checked by a licensed plumber.

Pressure Relief Valve Drain Line

The drain line is just as important as the valve.

A relief valve drain line should be:

Correctly sized
Safely routed
Not capped
Not blocked
Not damaged
Discharging to a suitable location
Installed with suitable materials
Visible where required
Protected from causing damage

Do not remove, block or redirect a relief drain without licensed plumbing advice.

Pressure Relief Valve for Indoor Hot Water Systems

Indoor systems need extra care because valve discharge or leaks can cause water damage.

Indoor installations may require:

Safe tray
Safe tray drain
Relief valve drain
Accessible valve location
Water damage protection
Suitable discharge route
Correct pipework materials
Compliance checks

This can apply to:

Apartments
Townhouses
Laundries
Cupboards
Internal garages
Under-stair locations
Ceiling or internal plant areas

A replacement hot water system may need drainage upgrades if the old setup is not suitable.

Pressure Relief Valve for Outdoor Hot Water Systems

Outdoor systems still need safe drainage.

Check:

Where the valve discharges
Whether water pools at the base
Whether discharge runs onto paths
Whether discharge damages walls
Whether discharge affects foundations
Whether discharge creates a slip hazard
Whether pipework is protected
Whether the discharge point is visible

Outdoor discharge should not be ignored just because the system is outside.

Pressure Relief Valve for Heat Pumps

Heat pumps commonly need pressure relief drainage plus condensate drainage.

These are different drainage needs.

Drainage Type	Purpose
Relief valve drain	Carries valve discharge safely away
Condensate drain	Carries normal heat pump condensate away
Safe tray drain	May be used for indoor or sensitive locations

When buying a heat pump, check both pressure relief drainage and condensate drainage.

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.

Pressure Relief Valve for Electric Storage

Electric storage systems commonly use pressure and temperature relief valves.

When replacing electric storage, check:

Existing PTR valve
Relief drain line
Water pressure
Pressure limiting valve
Expansion control valve
Tempering valve
Safe tray if indoors
Tank connection points
Valve rating
Pipework condition

A new tank may have different connection points, which can affect valve and drain pipework.

Pressure Relief Valve for Gas Storage

Gas storage systems also use relief valves and safe discharge.

When replacing gas storage, check:

Natural gas or LPG
Tank size
Relief valve rating
Relief drain line
Water pressure
Pressure limiting valve
Expansion control valve
Tempering valve
Gas fitting requirements
Flue or ventilation requirements if applicable

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

Pressure Relief Valve for Solar Hot Water

Solar hot water systems can reach high temperatures, so relief valve and drainage checks are important.

When working with solar hot water, check:

Tank relief valve
Solar collector valve requirements where applicable
Booster setup
Drainage
Existing valve condition
Safe discharge point
Whether roof components are staying
Whether solar pipework is being removed or isolated
Whether the system is being changed to heat pump, electric or gas

Solar hot water work can involve additional roof, lifting and plumbing requirements.

Buying a Pressure Relief Valve Online

Before buying a pressure relief valve online, confirm:

Hot water system brand and model
Valve type
Pressure rating
Temperature rating
Connection size
Thread type
System type
Storage tank requirements
Drainage setup
Whether additional fittings are needed
Whether a licensed plumber has confirmed suitability

Do not buy a relief valve based on appearance alone. The valve must match the system requirements.

What Else Might You Need With a Pressure Relief Valve?

A pressure relief valve may be only one part of the full valve setup.

Depending on the system, you may also need:

Tempering valve
Pressure limiting valve
Duo valve
Expansion control valve
Isolation valve
Non-return valve
Relief drain materials
Safe tray parts
Condensate drainage materials for heat pumps
Connection fittings
Pipework materials

The full set of required parts depends on the hot water system and property.

Common Mistakes With Pressure Relief Valves

Assuming Dripping Always Means the Valve Is Faulty

Constant dripping may be caused by high water pressure, expansion pressure, faulty pressure control or other system issues.

Blocking the Drain Line

Relief valve discharge should never be capped or blocked.

Ignoring the Discharge Point

Poor discharge location can cause damage, staining or slip hazards.

Buying the Wrong Valve

The valve must suit the system rating, connection size and application.

Reusing an Old Valve Without Checking

Old valves may be worn, corroded, seized or unsuitable.

Forgetting the Pressure Limiting Valve

High mains pressure can affect the relief valve and system.

Forgetting the Expansion Control Valve

Some storage systems may need expansion control on the cold water side.

Comparing Product Price Only

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

Not Using Licensed Trades

Plumbing work must be completed by appropriately licensed tradespeople.

Buyer Checklist Before Ordering a Pressure Relief Valve

Before ordering, confirm:

Hot water system type
Brand and model
Storage or instant system
Electric, gas, heat pump or solar setup
Valve type required
Pressure rating
Temperature rating
Connection size
Existing valve condition
Water pressure
Existing pressure limiting valve
Expansion control requirements
Drainage route
Safe discharge point
Indoor or outdoor location
Safe tray requirements if indoors
Whether extra fittings are needed
Licensed plumber requirements

Supply-Only vs Installed Cost

Hot Water Outlet sells supply-only hot water systems, valves and accessories online. Supply-only pricing is useful for comparing product costs, but it is not the same as total installed cost.

The final installed cost may depend on:

Licensed plumbing labour
Valve installation
Pipework changes
Drainage work
Existing valve removal
Access
Water pressure issues
Additional fittings
Safe tray work
Hot water system replacement
Electrical work if the system is being replaced
Gas fitting if gas is involved
Compliance upgrades

Where appropriate, Hot Water Outlet may help organise quotes from reputable installers.

FAQ: Pressure Relief Valves for Hot Water Systems

What does a pressure relief valve do on a hot water system?

A pressure relief valve helps discharge water when pressure needs to be relieved from the hot water system. Many storage systems use a pressure and temperature relief valve.

Is a PTR valve the same as a pressure relief valve?

A PTR valve is a pressure and temperature relief valve. Many people call it a pressure relief valve, but it responds to both pressure and temperature conditions.

Why is my hot water pressure relief valve dripping?

It may be normal expansion discharge, or it may indicate high water pressure, a faulty valve, debris, expansion control issues, overheating or another system fault. A licensed plumber should check it.

Can I block a dripping relief valve?

No. A relief valve or discharge pipe should never be capped, blocked or disabled.

Do electric hot water systems need pressure relief valves?

Many electric storage systems use pressure and temperature relief valves. The correct valve depends on the system rating and installation requirements.

Do heat pumps need pressure relief valves?

Heat pump storage systems commonly need pressure relief drainage and may also need condensate drainage. A licensed plumber should confirm the full setup.

Do gas hot water systems need pressure relief valves?

Gas storage systems commonly use relief valves. Instant gas systems have different valve requirements depending on the appliance and setup.

Can I reuse my old pressure relief valve?

Sometimes, but only if it is suitable, correctly rated, compliant and in good condition. Old valves may need replacement.

Is a pressure relief valve included with a hot water system?

Sometimes, but do not assume all required valves, fittings and drain materials are included. Check the product listing and confirm with your licensed plumber.

Can I install a pressure relief valve myself?

No. Plumbing work must be completed by appropriately licensed tradespeople.

Can Hot Water Outlet install a pressure relief valve?

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

Final Thoughts

A pressure relief valve is a key safety part on many hot water systems, especially storage tanks, electric systems, gas storage systems, heat pumps and solar hot water. When replacing a hot water system, the valve, rating, drain line, water pressure, expansion control and discharge point should all be checked.

Do not assume the old valve is suitable, and never block or ignore relief valve discharge.

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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