What Is a Pressure Release Valve? – Everything You Need to Know

James Elston
Written by James Elston
Updated on 18th January 2024
Posted on 17th January 2024
Topic: Boiler Advice
What Is a Pressure Release Valve

If you’ve got a boiler, it’s essential to know how the basics work. If something goes wrong on a Sunday night you might save yourself some serious repair costs if you know what to do in the meantime.

That’s where we come in. We’ve put together this guide on pressure relief valves, providing you with all the information you need. You’ll learn what a pressure relief valve is, how it works, what to look out for, and its benefits.

Let’s get going. 

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What Is A Pressure Relief Valve?

A pressure relief valve is used on a boiler to release pressure when the heating system reaches a certain level of pressurisation.

The valve opens when the boiler pressure gets too high and closes again once the water pressure releases to a safe level. 

Ensuring that the boiler pressure is what is should be is vital, as boilers and central heating systems can become unsafe if the water pressure reaches a certain point. Without a boiler pressure relief valve, you may be at risk of boiler explosions and leaks. 

Luckily most boilers would just lockout instead, however, you would have a boiler that doesn’t work at all in this case until fixed.

There are different types of pressure relief valves, the most common for a household central heating system are spring-loaded relief valves.

Now, let’s get into how a boiler PRV works. 

How Does A Pressure Relief Valve Work?

We’re looking at the most common boiler pressure relief valve, known as a direct spring-loaded valve. 

To know how the boiler PRV works we first need to look at the components:

  • Stem/spindle.
  • Pressure relief valve cap.
  • Calibrated spring.
  • Pressure relief valve seat/seal.

A boiler pressure relief valve has an inflow, once the pressure increases to a certain level the seat/seal pushes up the spindle/stem. 

The spindle/stem then pushes against the resistance of the pressure relief valve spring, which releases the water to the outflow. 

When the pressure lowers the seal/seat closes again to prevent the water from getting through the water outflow. 

Pilot-operated safety valves are used for boilers with high flow rates and extreme pressure. They have main and pilot valves.

The main valves work as above, while the pilot valves attach to the main line connecting to the main valve. Once the pressure level is exceeded the pilot valve opens to let the pressure out, causing the main valve to open.

Which Boilers Work With Pressure Relief Valves?

Essentially all modern boilers work using a pressure relief valve, whether it’s for domestic or commercial use. 

Some examples of boilers include:

Domestic gas boilers: These are the ones you’ll know most about because they’re in most UK homes in all the main boiler types such as combi boilers, system boilers and regular boilers. These are what produce hot water for heating your home through the circulation of the hot water around your radiators. 

Process boilers: These are used for various industrial uses like food processing and chemical manufacturing. 

Steam boilers: Generally found in factories, hospitals, and plants, steam boilers generate steam to produce power and heat. 

Whatever boiler you’re using, pressure relief valves are one of the most important safety components. So your boiler must have one in working condition, if not it may be time to consider a boiler replacement.

Benefits Of Using Pressure-Reducing Valves

Let’s explore how these valves benefit you.

  • Equipment protection: If there is a sudden rise in pressure there’s a chance your systems and equipment may be damaged. The pressure relief valve helps to protect your equipment in the event of too much pressure. Replacing equipment can be mighty expensive, a valve is a much cheaper solution. 
  • Money savings: If equipment fails and you’re out of business there can be massive ramifications. A valve is a fraction of the cost of a bad accident or flooding. 
  • Improved safety: Above all, the pressure relief valve is a safety mechanism. Whether you’re using a boiler for work or in your home, you can have peace of mind knowing you have the right parts to keep your equipment safe and in working order. 
  • Regulation compliance: Most industries require boilers to have pressure relief valves fitted for standard safety. To have boilers fitted they must have the correct pressure relief valves that meet regulations. 

Things To Look Out For On Your Pressure Relief Valve

As safe as a pressure relief valve is there are things to look out for if they go wrong:

  • Boiler Leaks: If you’ve already got a pressure relief valve set up and notice leaking you need to act quickly. The pressure build-up could be too much if the valve has failed leading to a leaking boiler. There should be minimal leaking if you’ve got a pressure relief valve set up correctly. Excess water is not normal and means there is too much pressure.
  • Corrosion: Unfortunately, rust can corrode your pressure relief valve causing it to fail. You need to inspect the valve every few months to check it doesn’t need replacing. 
  • Quality issues: Always buy your boiler parts from reputable suppliers. Also, ensure that you’re buying the correct pressure relief valve for the type of boiler you’re using. Substandard materials can affect the functionality of the valve. 
  • High pressure: The pressure relief valve removes the risk of high pressure in your boiler. If your valve malfunctions there could be a quick pressure build-up. This is a dangerous situation. Look out for unusual noises, leaking, and high-pressure gauge readings.
  • Blockages: When inspecting your valve keep an eye out for blockages. A technician will rinse your pressure relief valve and heating system with water to remove all dirt and debris. 

If you notice anything like this it’s best to call in a plumber to look at what’s going on. It may be tempting to open your boiler and have a look but you’re putting yourself at risk.

Remember, the water is extremely hot, so if you go anywhere near it you’ll need rubber gloves. Additionally, if there is a substantial leak ensure there is somewhere for the water to go like a large bucket.

The Pressure Relief Valve Location

Most pressure safety release valves are situated on the side of your boiler near the boiler’s water level. 

It attaches to a tube or pipe that goes down, ending close to the floor or a drain. This pipe keeps the hot water headed away from the boiler. 

It’s important to have the release valve installed by a professional to ensure it works efficiently while keeping things safe. 


How do I know if I need a pressure relief valve? 

Your combi boiler heating system should come with a relief valve. They generally need replacing every 4-5 years.

How do I know if my pressure relief valve is working?

You’ll know it’s time to replace your combi boiler pressure valve when your heating system can’t reach its maximum pressure, there is a leak, or the valve is going over the allotted pressure. This may also indicate a problem with your boiler’s expansion vessels.

How do I know which pressure relief valve my boiler needs?

The valves come in different sizes and types. That’s why it’s important to have a professional look at your system. Replacing pieces yourself can be dangerous, particularly when dealing with high-pressure boilers.

Is it important to have the right size valve? 

Absolutely! Fitting the wrong size valve to your boiler can be seriously bad news. Too big and it simply won’t hold pressure, too small and you’re at risk of major pressure build-up without adequate pressure release. 

Wrap Up

A PRV valve is an essential part of your boiler. Before they were around, a pressure build-up in your boiler was a very serious issue.

Pressure in any form can be a disaster. It can damage your equipment and other systems in the home if you don’t realise something has gone wrong in time. That’s why every boiler needs to have a pressure relief valve.

Written by
James Elston
James Elston Director Of Boiler Central
Posted on: 17th January 2024
Topic: Boiler Advice

James Elston is our resident boiler replacement and heating expert here at Boiler Central. With over 20 years experience in the boiler installation industry, James ensures that he knows everything there is about our Gas Safe boiler installations, energy saving and home heating solutions. This can be from simply procuring the latest best combi boilers, to reviewing and ensuring that Boiler Central maintains the highest standards across our boiler installation company.

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