Boiler Pressure Relief Valve Keeps Going Off – What to Do?

One of the most common call-outs for our engineers relates to boiler pressure relief valves that are constantly blowing off. Generally speaking, this is not a significant issue, but it can be annoying if you have guests staying over or need to get your boiler serviced. What’s more, there are fixed penalties for something that is largely preventable, and in many cases, it’s simply down to an easily correctable fault with your system.

We’ll cover some of the root causes in detail below and explain what we recommend you do if boiler pressure relief valve keeps going off:

Boiler Pressure Relief Valve Problems

Why Does My Boiler Keep Blowing Off?

There are several reasons why this might happen, but generally speaking, a boiler will release its pressure when it detects too much gas in the system. This often occurs when you have been using your heating system for a long time without switching it off and simply letting the heat build-up in your radiators. Similarly, if you switch your heating on again before the pressure has had a chance to escape, then you could find that you experienced this problem.

However, other problems could be responsible for your boiler blowing off its pressure, including:

  1. Carbon monoxide poisoning – The build-up of this poisonous gas can cause serious health issues if it leaks into a sealed room and people breathe in the fumes. If this has happened, close down all of your appliances until an engineer has checked it out.
  2. Leaking boiler flue – This is a very common problem and can easily be solved by getting a repair or preventative maintenance plan in place to avoid this sort of thing from happening in the future.
  3. Faulty pressure relief valve – Check a defective relief valve, but if you have, then this would be an excellent way to solve the problem by simply having one fitted that isn’t faulty.
  4. Boiler pressure too high – If your system is pressurized beyond its normal limits, then it’s probably time to get an engineer involved because there might well be something wrong with your boiler, which means it needs adjusting.

How Can I Solve The Problem?

There are several ways for you to solve the issue of your boiler pressure relief valve blowing off repeatedly. Some are relatively simple solutions that could save you a fortune in repair bills, and others will involve getting in touch with a plumber.

Turn your heating down – If there is too much heat in your system, then it’s going to struggle to maintain an even temperature, and so this is likely to result in over-pressurization. Simply turning the dial back on your radiators should be enough to keep things under control.


I have recently had this same issue with my boiler, so I researched the problem. It seems that the pressure relief valve itself is perfect, but there is also a mechanical valve (which looks like the same thing) that can go wrong. If your pressure relief valve keeps blowing off, then that’s an excellent place to start checking.

FAQs about Boiler Pressure Relief Valve

What causes a pressure relief valve to go off?

There are a few different reasons pressure relief valves go off. The most common of these is when people turn on the faucet while filling up their sink with water or getting ready to shave. Another way that causes people’s PRVs to go off is when they turn on an appliance, like, say, the dishwasher, and then decide they don’t want to use it anymore without closing the door again.

What causes too much pressure in the boiler?

The pressure can be caused by too much steam being pumped into the boiler, thereby exceeding the safe boiler capacity. Another possibility is that some debris (e.g., dirt) was found in the boiler’s high-pressure feedwater line and has cut off flow to one of the smaller pipes feeding water to the small boiler tubes which heat upon contact with this hot steam above them; or continued flow through corroded or plugged small pipe could ultimately lead to a hydraulic lock-on.

How often should pressure relief valves be replaced?

Pressure relief valves should be replaced when they are constantly leaking. It is not advisable to continually replace them because the valve may go out at any moment, and then you will find that you need more than one.

Should the pressure relief valve be up or down?

It should be up. The relief valve is designed to protect the tank, not people. If it’s designed to keep the tank from exploding, then that’s where it needs to go.

A correctly installed pressure relief valve will be installed with its top pointed towards the ground, and its outlet pointed upwards. This way, gasses can escape on their own, and atmospheric pressure will help remove them more quickly than water would do on its own. This avoids situations of bubbles forming above a person’s head and bursting as they go up for air, which could send burning gas raining down on them or anyone else nearby. 

How do you test a relief valve?

You can test a relief valve with some soapy water and a really long straw.

Step 1: With the valve closed, put soapy hands on both sides of the pipe and blow through it.

Step 2: Turn off one end of plumbing’. If there is a leak, bubbles will appear at the other end. The size of the bubbles tells you about how much air is leaking – large or small bubbles indicate more or less air escaping respectively.”

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