What Does a Pressure Relief Valve Do?

A pressure relief valve is one of those tiny components within your boiler that plays a critical role in ensuring that everything continues to function efficiently. The pressure relief valve prevents the boiler from shutting down or alternatively displaying a permanent fault code by avoiding the build-up of pressure

Pressure Relief Valve: What Exactly Does It Do?

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.

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. 

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 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. 

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.