What pressure should my boiler be set at?

What is boiler water pressure?

Your boiler heats cold water, then sends that hot water around your home’s circuit of pipes and radiators. For it to work as efficiently as possible, you need stable water pressure within the system.

If your boiler isn’t working properly and you’re not getting hot water as normal, you’ll often find the problem is your boiler pressure is too low, or sometimes too high.

Luckily, it’s usually quite easy to diagnose and fix problems with boiler pressure.

Why do boilers lose pressure?   

Bleeding radiators

One of the most common causes of pressure loss is if you’ve recently bled your radiators. As air is released from your central heating system, it lowers the pressure. So make sure you check the pressure gauge after bleeding a radiator.

Leaks in your central heating system

There could be a leak in the pipes or valves anywhere around your home. It can be tricky to pinpoint where the leak is coming from and if you don’t get it fixed, your boiler will continue to lose pressure. If you think you’ve got a leak, get an expert to fix it – that’s something we can help with. In fact, if you’re already a HomeCare customer then you can simply log in to your account and book an engineer. If you’re not – don’t worry, you can still get a one-off boiler repair from one of our trusted engineers.

How to check the pressure of other types of boilers

If you have a water tank and hot water cylinder, you have either a conventional or system boiler. In some cases, you will have a pressure gauge on the boiler itself. But you might find your boiler pressure gauge near your hot water cylinder, usually near a smaller red vessel.

What’s the right boiler pressure?

It’s perfectly normal for your boiler pressure to vary a little. Pressure increases when the water gets hot and decreases when it cools down. But your pressure should always be somewhere between 1 and 2 bar.

If your boiler pressure reads less than 1 bar, you might have lost water from the system, and this will need to be replaced. If it’s above 2.75 bar, that’s a sign of high pressure – and the best way of bringing that down is to bleed a radiator.

How to increase boiler pressure

Pressure loss is the most common boiler pressure problem you’re likely to come across. It might happen a couple of times a year, but it’s very easy to fix.

If you have a system or conventional boiler with a boiler pressure gauge near your hot water cylinder, you’ll have a valve in the pipework – usually near the red vessel and the pressure gauge. Just open this valve a little and you should see the pressure gauge rise. Keep filling until it’s between 1 and 1.5 bar, then close it.

If you have a combi boiler, just follow these step-by-step instructions:

• Switch off your boiler and allow it to cool
• Double check that both ends of the filling loop are securely attached
• Open both valves (or just one, if that’s what your filling loop has) to allow cold mains water into the system. Listen out, you should hear it
• Wait for the boiler pressure gauge to reach 1 to 1.5 bar
• Close both valves, one after the other (or just the single valve, if that’s what you have)
• Switch the boiler back on. If needed, press the reset button
• Undo both ends of the filling loop and remove. Be careful to catch any water spillage and keep the filling loop in a safe place

This advice will help if you have the most common type of filling loop (pictured). If you have a different type or if you’re unsure, please check the user instructions for your boiler. You can usually find these online if you no longer have your printed copy.

Why does my boiler pressure keep dropping?

If your boiler pressure is dropping, it could be due to a leak in the system, faulty pressure valves or air escaping from radiators. However, if your boiler is still losing pressure, you might not be able to find a fault. Which can be very frustrating, especially if you’re left with no heating or hot water. 

Is low boiler pressure dangerous?

Low boiler pressure won’t harm you physically, so you don’t have to worry about that. The main danger is that it can harm your heating system. This could include reducing the efficiency of your boiler, making it louder and impacting the amount of hot water you get. In the long run that could cause more damage to your boiler and heating system and also see your energy bills increase. So it’s always advisable to get a gas safe engineer round to fix it.

How to reduce boiler pressure

Boiler pressure being too high is a more unusual problem.

One simple thing to check is that the pressure valves under your boiler are closed tightly. If they become loose accidentally, this can cause your boiler pressure to become too high.

Another thing you can do to release boiler pressure without touching the boiler itself, is to bleed a radiator. This video shows you how to do it yourself, but if there’s still a boiler pressure issue, it’s time to get expert help.

Unless you’ve accidentally overfilled the system yourself, it could be a sign of a more serious issue. If you leave it too long it could cause serious damage to your boiler and central heating system. Make sure you get it repaired by a gas safe engineer.

How to release pressure from boilers

It’s understandable that you want to release pressure from your boiler to make sure it doesn’t cause any damage to you or your household. And while it may seem straightforward to do, especially if you find DIY guides online, it’s not something we recommend. If it’s not done the right way, hot water could come gushing out…and we’re talking about temperatures as high as 70°C to 80°C. So that would scald and leave some nasty damage. To top it off, you could also damage the boiler and pipes if it’s not done properly. There are some preventative measures you can take – here’s what we recommend:

• Turn off your boiler
• Locate the pressure release valve
• Place a container underneath to catch any leaking water
• Get in touch with us so an engineer can come to fix it

How to lower pressure without bleeding radiators?

Bleeding radiators is the easiest way to lower your boiler pressure without having to touch the boiler itself. But if that doesn’t work, you might be tempted to look into other ways. Some of these methods may include adjusting the pressure relief valve on the boiler to see if that helps, or by draining water from the system. However, these can be tricky jobs and should be left to the professionals. Good job that British Gas has thousands of engineers across the country – so if you need to lower your boiler’s pressure, we can help.