What to do if your boiler loses pressure?

Do you know what to do if your boiler loses pressure? If you’re concerned that your boiler pressure keeps dropping, read on to find out the reasons why it’s dropped and what you can do.

Why does my boiler keep losing pressure?

You may be wondering why your boiler keeps losing pressure, but you’re probably also wondering why boiler pressure is even important in the first place?

You’ll be well aware that your boiler system contains water that gets heated up, and this water is pumped around your central heating and hot water system to keep your water and home toasty warm. The boiler pressure is important as it is the pressure that helps to keep that hot water going to where it is needed and your hot water and heating system working efficiently. If your boiler is losing pressure there can be a few common causes.

Common causes for boiler losing pressure

The most common causes for a boiler losing pressure are:

• Leaks
• Bleeding radiators

If your boiler pressure keeps dropping the culprit may be a leak somewhere in your central heating or hot water system.

When you think of a leak, you might be imagining a large-scale leak with water gushing from a pipe. Those leaks will of course cause your boiler to lose pressure, but more common is a small or ‘slow’ leak that could be the size of a pinhole. These kinds of small leaks cause a gradual loss of pressure that eventually causes your boiler to stop working properly.

To find out if you have a small leak, look for damp patches under radiators or pipework, or underneath where your boiler is located. If you check your boiler pressure regularly, you may also notice the pressure reducing over time.

Your boiler losing pressure may also be the result of bleeding your radiators. When a radiator is bled air is also released. If you have bled multiple radiators recently, then enough air may have been released during the bleeding process to cause your boiler to lose pressure.

To check your boiler pressure there is usually a pressure gauge that looks like a dial with an indicator needle. This gauge is normally towards the front or just underneath your boiler.

When the boiler is idle and your radiators are cold, you can expect the pressure to be just above 1 bar. When your radiators are hot you can expect the pressure to be at approximately 2 bar.

The normal pressure range for a boiler is between 1 to 2.5 bar, so if your boiler pressure drops below 1 bar, there is not enough pressure to keep the hot water flowing around your heating system.

Repressurising your boiler

It’s usually possible for you to repressurise your boiler following the instructions for your specific make and model. These instructions should be available in your boiler manual or can be found online.

For more information, you can also read our guide ‘How to repressurise a boiler‘.

Why is my combi boiler losing pressure?

Your combi boiler might be losing pressure if there is a problem with a part called the pressure relief valve (PRV).

If you have had a continuous flow of water running through this valve then debris or build-up may cause this valve to get blocked. As this valve is a crucial part of your boiler system, if this part fails then so will your boiler.

Check your boiler’s safety discharge pipe (usually located outside on the wall where your boiler is installed) and if this pipe is dripping or has water leaking from it, there is a good chance there is an issue with the pressure relief valve.

Your combi boiler losing pressure may also be as a result of air in the system or due to a leak as we talked about above. Check for signs of water around your pipework and radiator valves, as well worktops or kitchen cabinets which might tip you off that there is a leak.

To prevent issues like this from cropping up, it’s always recommended to get your boiler serviced annually by a CORGI registered heating engineer.

Why is my gas boiler losing pressure?

The most common reason for a gas boiler losing pressure is a problem with a safety device or a faulty part.

The first thing to do is check your boiler’s display panel to see if there are any error codes. Check these against your boiler manual or you can look them up online.

Another thing to check is whether your boiler pilot light has gone out. If the pilot flame is out then your boiler will have stopped working. If you can’t see the blue flame or if your boiler panel indicates that the pilot light has gone out, then take a look at our blog about what to do if your boiler pilot light has gone out.

If it’s still not clear what the problem is then it’s time to call on the help of a professional.

Why is my boiler losing pressure but no leak?

If you’ve tried to be a detective and can’t find a leak but your boiler is still losing pressure, then there is either a faulty part causing the issue such as a faulty pressure gauge or pressure relief valve.

Boilers expand and contract as they heat and cool and work pretty hard, especially in winter, so there may be other internal issues inside your boiler that are the cause of the problem.

The best thing to do if your boiler pressure keeps dropping is to get in contact with a heating engineer to diagnose and repair the problem.

If your boiler is getting old and consistently loses pressure then it might be time to invest in a replacement.

For an idea on cost, take a look at our boiler cost guide.