Issues with your boiler pressure?

One of the main reasons for boiler breakdowns is pressure loss. Low boiler pressure can cause your boiler to work ineffectively, making it more difficult to warm up your home. Learn what pressure your boiler should be, signs it is either too high or low and your options if it needs to be fixed.

Maintaining boiler pressure for optimal usage

The last thing you want when returning home from a long day is no hot water or heating due to a broken down boiler. As well as age and frozen external pipes, losing boiler pressure is one of the main causes of boiler problems in the UK. Losing boiler pressure can result in your boiler having to work harder to warm up your home which can have an impact on your energy costs.

Safety first

Concerning boiler issues, we always recommend that you call a Gas Safe engineer to inspect the problem. There are a few checks you can undertake yourself before calling in the professionals, but only if you feel confident to do so. 

Our guide on managing your boiler pressure

Modern boilers are highly efficient, better for the environment and allow for improved heating control, which helps lower your energy bills. However, sometimes even modern boilers break down, which is never ideal. There can be many reasons for a boiler breakdown, with boiler pressure being one of the most common. We’ve provided a guide to help you to understand what pressure your boiler should be, as well as how to fix it when it’s too high or low. Thankfully, diagnosing boiler pressure issues can be relatively simple and often easily fixed yourself.

Why is boiler pressure important?

For central heating to effectively warm up your home, your boiler needs to have the right amount of pressure to circulate hot water. This makes boiler pressure important for various reasons. As your boiler heats cold water, the water expands in pipes and radiators throughout your home. This is why you may notice a difference in your boiler pressure when the heating is on versus when it’s off. It’s important to maintain a stable pressure for your boiler to work efficiently. An unbalanced water to air ratio can result in the system becoming over pressurised and possibly result in a breakdown.

What pressure should my boiler be?

The correct boiler pressure changes for different systems. Usually the pressure should be between 1 and 1.5 bar, with 1.3 being recommended by most manufacturers as the optimal pressure when the boiler is off. It’s best to check your boiler manual or contact the manufacturer to confirm the optimal pressure for your boiler, for example, the optimal boiler pressure for a Worcester Bosch boiler is 1.5 bar. You can also check your boiler pressure by looking at the built in boiler pressure gauge (circled in blue). Most boilers highlight the optimal pressure in green, with a needle indicating what your current boiler pressure is.

What pressure should my boiler be when heating is on?

When the heating is on, your boiler pressure should be between 1.5 and 2. As mentioned above, you can check this on the boiler screen or pressure gauge to see if the gauge needle is within this area, which is usually highlighted in green.

What happens if boiler pressure is too high?

High boiler pressure is inefficient but rarely dangerous, as most modern boilers have a safety feature known as the ‘pressure relief valve’ that shuts down the boiler to prevent further pressure from building. 

However, if the pressure relief valve itself is faulty or broken then we’d strongly recommend you call a Gas Safe engineer straight away to take a look as there is the possibility it could become dangerous, for example if the valve becomes clogged, pressure will build up and could potentially risk a boiler explosion. More commonly, the system could become over-pressurised and break down, leaving you with an expensive repair job or the cost of a new boiler altogether. There are three signs that your pressure relief valve is faulty or broken:

  1. Your boiler system fails to reach pressure and could have been set to the incorrect set pressure and is releasing early
  2. Your system is above pressure and your pressure relief valves have not released
  3. The pressure relief valve has a leak or is not showing any pressure at all

If boiler pressure fixes you carry out yourself don’t work, such as checking the filling loop valves or bleeding the radiators or if you spot any of the signs above that your pressure relief valve is faulty, it’s best to call out a Gas Safe engineer to check the problem. 

Why is my boiler pressure so high?

There are three main reasons for a boiler pressure being too high. 

Too much water in the system

If you have recently repressurised your boiler due to low pressure, you may have let out too much air from the system and need to drain out some water. 

Faulty boiler parts

Most modern boilers include a pressure relief valve that automatically releases pressure once it rises above the optimal pressure. If this valve is faulty, your boiler may lose pressure. 

Boiler wear and tear

If you’ve had your boiler for a long time it may just be wear and tear issues. It’s recommended that you change your boiler every 10 years so look into comparing offers for a new boiler.

How to check why your boiler pressure is too high

When your boiler pressure is too high, there is a way for you to check where the problem is coming from. Check around your home to see whether you can spot any visual leaks from pipework. Look around the boiler, pipes and radiators for any signs of a leak as well as damp patches or water around your home. It is not recommended to check inside the boiler for leaks, rather call a Gas Safe engineer out to examine it.

How to reduce boiler pressure

You can bleed or drain water from your radiators but if you don't feel confident in doing this our best advice is to call a Gas Safe registered engineer to look at your system.

Why is my boiler losing pressure?

There could be a water leak in either the boiler or its pipework, meaning water is draining from the system and, in turn, lowering the boiler pressure. These leaks might only be minor, for example a small leak on a radiator valve, but over time they can affect the efficiency of your boiler as well as cause a drop in pressure.

How to repressurise your boiler system

There are two methods of topping up your system, depending on the type of boiler that you own and also which option your installer may have chosen for you. Watch the videod below for advice. If you get stuck, contact your boiler manufacturer for further guidance. It‘s a good idea to check your boiler pressure every month to make sure it‘s running efficiently and avoid unexpected breakdowns. 

Repressurising a boiler using the Filling Key

The first option is using an internal filling key. Watch the video below to see how to top up your boiler system using an internal filling key.

Repressurising a boiler using the Filling Hose

The second option is to use the external filling hose. Follow the steps shown in the video below to top up your boiler system using this method.

Need a boiler service?

If you have tried these fixes but you still have problems with your boiler pressure, you should contact a Gas Safe engineer to take a look and diagnose the problem. 

To avoid high one-off repair costs, you can also take out boiler cover for your existing boiler, where a boiler service will often be included in your policy. For boiler cover that includes both servicing and breakdowns, check out your cover options with our partner, HomeServe, from just £7.99 per month.

Thinking of buying a new boiler?

We offer an exclusive boiler service plan in partnership with Worcester Bosch when you buy a new boiler from us, For £396, you can relax knowing your boiler servicing is covered for three years.