How to fix a leaking boiler pressure relief valve

Boiler pressure is determined by the level of water and gas within the unit. It’s essential for this to be balanced to ensure proper functionality and safety. As such, all residential and commercial heating systems will contain some form of pressure relief valve. Regardless, the application and presence of boiler pressure valves is of great importance, so must be fixed immediately when there is a fault.  

In this blog, we’ll be covering recognising a malfunctioning boiler pressure relief valve, and how a leaking one can be fixed. 

What does a boiler pressure relief valve do? 

Boiler pressure relief valves are safety measures designed to prevent the build-up of pressure within the boiler. It does this by monitoring internal pressure levels and allowing for the safe exit of pressurised fluids from the system. Excess pressure within a boiler can lead to costly damages, shut down, or even hazardous rupturing. 

The pressure relief valve can vary in its location depending on the boiler make and the layout of the property. However, it’s usually positioned inside the casing at the bottom, or on the side close to the water level. It will also likely be positioned close to the mains water supply. In either case, it will connect to copper or PVC tube that travels downwards from the boiler unit. 

Most pressure relief valves contain a spring-loaded mechanism to allow for pressure reduction. The force of the pressure simply forces the valve open, leading the fluid or steam away from the boiler. Then, once the pressure has been reduced to satisfactory levels, the spring causes the valve to close. 

Spotting a faulty pressure relief valve 

A defective boiler pressure relief valve can be indicated in a few ways. The first is through audible stress being exerted on the boiler unit. This is due to steam build-up, caused when it is unable to escape the interior of the boiler. The result is a rattling or whistling sound heard coming from the unit. 

Second, if you notice a loss of boiler pressure, this could be caused by faults associated with the pressure release valve. For instance, a blockage around the valve that prevents it from closing fully. In this case, pressure is constantly being allowed to exit the system. A boiler blockage can be caused by either a concentration of debris or limescale interfering with the mechanism. 

Last, leaks can be an indication that something is wrong with the boiler’s pressure relief valve. A leaking boiler is often evidence of an unhealthy amount of pressure build-up, resulting from a defective pressure relief valve. As a reverse of the above scenario, this will occur when the valve is prevented from opening. 

Fixing a leaking pressure relief valve for boiler 

It is extremely important to fix a malfunctioning pressure relief valve as soon as it gets noticed, especially if it results in a boiler leak. As mentioned above, this is because the valve is causing the pressure within the boiler to rise. Fixing or replacing the pressure relief valve is a far more cost-effective option than having to get a replacement boiler due to ruptures. Not to mention the additional inconvenience of a loss of heat resulting from boiler breakdown. 

Fixing a leaking pressure relief valve is also an important safety measure to protect other internal boiler components. In fact, many industries make sure all heating systems are fitted with pressure relief valves as standard. Taking all of this into account, it is recommended that boiler pressure relief valves are fitted by a qualified professional. They will likely do the following: 

• Turn off the fuel supply. 
• Turn off the water. 
• Undo the nut connecting the pressure relief valve to the outflow pipe. 
• Loosen the pressure relief valve grub screw and remove the part. 
• Fit a new valve, tighten the grub screw, and reattach the pipe. 
• After all nuts and screws have been tightened, the boiler can be repressurised. 
• All radiators in the build must be bled. 

It should also be noted that boiler pressure relief valves come in a range of sizes. It’s important that the correct size is fitted to the boiler to ensure an efficient transfer of pressure. Too big and the boiler won’t maintain pressure, too small and there is significant risk of dangerous pressure build-up. 

Boiler parts UK 

National Boiler Spares has a vast range of boiler parts, including boiler pressure relief valves in a range of makes, models and sizes. All our stock is certified to BSI ISO 9001:2015 and BSI ISO 14001:2015 standards. Our catalogue is also simple to navigate, making it quick and easy to find the parts you need. Once ordered, we have many flexible delivery options to suit you. Contact us today.