Everything You Need to Know About Boiler Pressure Relief Valves: How to Install, Inspect, and Troubleshoot for Optimal Performance

What is a Boiler Pressure Relief Valve?

A Boiler Pressure Relief Valve is a safety device that prevents the boiler from exceeding its maximum safe pressure limit. It is typically installed on the boiler’s pressure vessel or a connected piping system and is set to open and discharge water or steam if the pressure within the system exceeds a pre-set limit.

The pressure relief valve is a critical component of the boiler system, as it protects against potentially dangerous situations such as boiler explosions or damage to the system due to high pressure. The valve is typically set to open at a pressure slightly above the maximum safe operating pressure of the boiler. It is designed to discharge excess pressure until it drops below the set limit.

Boiler pressure relief valves are typically designed and installed in compliance with industry standards and regulations, and their operation should be periodically tested to ensure proper functioning. Regular maintenance and inspection of the pressure relief valve are also necessary to ensure that it operates correctly in an emergency.

In summary, a Boiler Pressure Relief Valve is a crucial safety device that helps to protect the boiler and its associated piping systems from potentially dangerous situations by releasing excess pressure from the system.

Another description of a pressure relief valve would be a safety release valve, which demonstrates one of the critical benefits of this vital component. Pressure is essential to ensuring that your boiler can circulate hot water around your home, but that pressure needs to be maintained within specific levels to maximise the efficiency of the boiler and ensure that it is operating safely.

Unfortunately, PRV’s do become faulty and can be the cause a central heating system leak.

Pressure Relief Valve: What Exactly Does It Do?

The valve operates by opening up to release pressure when it senses that the levels have become too high and then closes once the levels have dropped to the correct level. These valves are used in a wide range of different appliances ranging from boilers through to equipment in the power generation industries. 

The most popular type of valve used in modern boilers is a spring-loaded relief valve. This valve incorporates many different features, with the main ones being a spring-loaded valve, a spring, and a sensor in the form of a piston.

Whenever the valve identifies that the pressure is building, the spring controls the valve by preventing the hot water or steam from passing through. Once the pressure reaches a tipping point that is greater than the force the spring can withhold, the valve opens up, releasing the pressure and allowing the water or steam to pass through. Once the pressure has dropped, the spring then shuts the valve creating the required seal. 

Types of Boiler Pressure Relief Valves

There are several types of Boiler Pressure Relief Valves available on the market. Here are some of the most common types:

Spring-Loaded Pressure Relief Valve

This is the most common type of pressure relief valve used in boilers. It consists of a spring that is compressed by the pressure of the fluid, and when the pressure exceeds the set limit, the spring expands, opening the valve to release the excess pressure.

Pilot-Operated Pressure Relief Valve

This type of valve uses a small pilot valve to control the opening and closing of the main valve. The pilot valve is connected to the main valve through a pipe, and when the pressure exceeds the set limit, the pilot valve opens, causing the main valve to open and release the excess pressure.

Balanced Bellows Pressure Relief Valve

This type of valve uses a bellows element that is balanced against the inlet pressure. When the pressure exceeds the set limit, the bellows expand, opening the valve to release the excess pressure.

Power-Actuated Pressure Relief Valve

This type of valve uses a power source such as compressed air or electricity to control the opening and closing of the valve. When the pressure exceeds the set limit, the power source activates the valve to release the excess pressure.

Thermal Expansion Pressure Relief Valve

This type of valve is specifically designed for hot water boilers. It uses a thermal element that expands when the water temperature exceeds the set limit, opening the valve to release the excess pressure.

Each type of pressure relief valve has advantages and disadvantages, and the selection of the appropriate type depends on factors such as the type of boiler, operating conditions, and safety requirements.

What Would Be The Reason For A Pressure Valve to Leak? 

Your boiler’s pressure release valve is constantly working throughout the day, and over time it is reasonably common for it to develop a leak.

The leak can be caused by a range of different factors, including but not limited to a build-up of limescale, the perishing of the seal around the edge of the valve, or a build-up of debris sludge or rust within your system. A blockage in the valve would prevent it from closing, meaning that it is unable to form a proper seal.

There are a number of reasons why you have found that your boiler has stopped working – the PRV is just one of them.

A leaking PRV is often found to following a boiler losing pressure. The boiler error codes F1 Boiler Fault Code, F22 error code, F75 fault or the E119 Error Code. are all signs of low boiler pressure.

A qualified heating engineer should be able to clear any blockages, although, in this situation, it would be advisable to flush the entire system, as otherwise, the valve is likely to become blocked again very quickly. 

Another option that your heating engineer may advise is the replacement of the pressure release valve. If you have recently had your pressure release valve replaced, and the problem persists, then there may be an issue with your boiler’s internal expansion vessel.

When your boiler heats cold water, physics dictates that this water will expand, causing the pressure to increase. The role of the expansion vessel is to provide additional space to cope with this expansion. If you have eliminated the pressure release valve as the source of the issue, then the next area to investigate is the internal expansion valve. This will require a visit from a qualified heating engineer. 

Common Problems with Boiler Pressure Relief Valves

Like any mechanical component, pressure relief valves can encounter problems affecting their operation and compromising the system’s safety. Here are some common issues with boiler pressure relief valves:

1) Valve leakage: A pressure relief valve that leaks can be a significant problem. If the valve is continuously leaking, it can cause the system to lose pressure, which can cause other components to fail. Leaking can be caused by a faulty valve seat or a damaged valve disk, which can be repaired or replaced.

2) Valve chatter: When the pressure relief valve rapidly opens and closes, it produces a hammering or rattling sound. This phenomenon is called “valve chatter.” Several factors, such as system pressure fluctuations, improper valve sizing, or incorrect installation, can cause valve chatter.

3) Improper pressure relief valve setting: Pressure relief valves must be set to the correct pressure to ensure safe operation. If the valve is set too low, it may not release pressure when necessary, and if set too high, it may release the pressure too early, which can cause unnecessary wear on the valve and affect the system’s efficiency.

4) Corrosion: Corrosion can cause damage to the valve seat, valve disk, or other components of the valve, which can cause the valve to fail to operate properly. Regular inspection and maintenance can help prevent corrosion.

5) Improper installation: Pressure relief valves must be installed correctly to ensure proper operation. Improper installation can cause the valve to leak, chatter, or malfunction, compromising the system’s safety.

Regular inspection, maintenance, and testing of pressure relief valves are essential to ensure that they operate correctly and reliably. If you encounter any problems with your boiler pressure relief valve, it’s vital to have it inspected and repaired by a qualified technician.

Is The Pressure Relief Valve A Replaceable Component on a Combi Boiler?

The good news is that it is a relatively easy job to replace the pressure valve, although it will require a Gas Safe registered engineer to complete the task.

In preparation for the Gas Safe engineer’s arrival, our advice would be to turn off the boiler a few hours before their arrival to give the boiler time to cool down.

Upon their arrival, the engineer will drain the system and then replace the pressure valve. The entire process shouldn’t take too long, and then your heating and hot water should be functioning properly once again. 

What is the Recommendation for Replacing the Pressure Relief Valve?

As part of your annual boiler service, the pressure relief valve should be tested annually, and it should be changed every three to five years. If a leak develops or you are constantly having issues with the valve, then it may need to be changed earlier.

The water hardness where you live will also have a bearing on the frequency of the change. For peace of mind, a qualified heating engineer can inspect the valve for you and let you know when he or she thinks it will need to be replaced.

Adrian Morgan

Adrain Morgan CIPHE RP RHP is the founder & Managing Director of ADI Pro Leak Ltd. Adrian is also the Head Plumbing, Heating & Leak Detection engineer at ADI Leak Detection.

Adrian CIPHE RP RHP is proud to be registered with the Chartered Institute of Plumbing & Heating Engineering, a Registered Plumber and a Registered Heating Professional.