What should your boiler pressure be?

If your boiler keeps losing pressure, it could be a simple fix or it could be an indicator that you need to call the experts in. Either way, here’s how to check your boiler pressure and what you can do about it.

Bear in mind that if you're not a trained heating professional, you should never attempt any repairs that involve removing the boiler casing. 

It's dangerous to do so and also invalidates any warranty you may have remaining on the boiler.

Need to call in the experts? Find a vetted Which? Trusted Trader in your area.

Setting the right boiler pressure

Most boilers will have a pressure gauge on the front somewhere (unless you have a very old tank system) and this will indicate the pressure of your boiler.

If you have a very old boiler, or a system boiler, the pressure gauge may be on the pipework somewhere.

For combi boilers, your boiler pressure should sit somewhere between 1 and 2 bars.

If it's below 1, your boiler won't be able to work properly and you'll start to see error messages or experience problems (see more below). 

If it's higher than 2, bleeding your radiators can help relieve pressure and get it back to the right level.

Why does my boiler keep losing pressure?

If your boiler loses pressure it could be down to a few things. 

It can happen if you've recently bled your radiators and need to reset the pressure. It can also happen when your heating has been off for a very long time, as this can cause a boiler to lose pressure gradually. It could also be due to a leak, which could be more serious. 

Most boilers will need to have their boiler pressure reset once or twice a year, and you can usually do this yourself. If you find yourself with a boiler with pressure that needs resetting regularly it’s probably time to call in an expert.

Get ahead of the cold weather, read our guide to getting the best boiler service to make sure your boiler is running as efficiently as possible.

How to increase boiler pressure

Your boiler’s pressure needs to be increased if the measurement on the gauge is below the recommended level (less than 1 for a combi boiler). You’ll probably need to do this if you’ve just bled your radiators, as this lowers pressure across your heating system.

The best piece of advice is to follow the manufacturer's instructions on how to do this. 

You can increase your boiler's pressure yourself if you know what sort of filling system you have - an internal loop or external loop. Your instruction manual should tell you what type you have and how to top up the boiler’s pressure. 

If you've lost the manual, you may well be able to find instructions online or the manufacturer should be able to talk you through it over the phone. 

If you’re unsure, contact your boiler manufacturer or a qualified heating engineer.

Read more in our guide to dealing with common boiler problems. 

Is low boiler pressure dangerous?

Low pressure isn’t dangerous but it can be problematic, because it will mean your boiler isn’t working as efficiently as it could, so it will end up costing you more on your heating bills due to using more energy – and more expensive energy bills are something none of us wants. 

It may also cause damage to your heating system if the underlying cause isn’t resolved. 

Always check your boiler instruction manual first, as some systems can have different instructions. 

Repressurising a Worcester Bosch combi boiler has slightly different instructions. You can see full details for how to repressurise a Worcester Bosch boiler on its website.

How to lower boiler pressure

If your boiler pressure is too high you’ll usually be able to see from your boiler’s pressure gauge (if it has one) or your boiler’s display screen, which may show an error code. 

Some boiler manufacturers say you may also see leaks or drips from your system. 

There are several ways to lower pressure in your heating system. You can bleed your radiators to remove water from the heating system – this is a fairly simple task which you can do at home. 

Check our guide to bleeding your radiators for more details.

If you have a combi boiler and its pressure is too high, check that the filling loop hasn’t been overfilled or that the valve has been left open. 

Ideal Heating suggests turning the valve by 90 degrees to make sure it’s closed, or checking to see if the handle is aligned with the pipe (this means it’s open and will need closing). 

British Gas also advises checking the pressure valve under your boiler is closed tightly. 

If you’re concerned about high boiler pressure and it hasn’t been fixed by bleeding your radiators, call in a Which? Trusted Trader expert to check it out. 

What should boiler pressure be when heating is off?

When your boiler is off, the pressure displayed should usually be around 1 or 1.5 bars. 

Check your boiler’s instructions to see what’s typical for the boiler you have.

If you decide it's time for a new boiler, make sure you buy from the best gas and oil boiler brands.