Resolve your boiler pressure issues

Modern boilers are highly efficient, better for the environment and allow for improved heating control, which helps lower your energy bills. But for boilers to perform efficiently, they need to operate at optimal pressure – and sometimes even modern boilers can break down. We’ve provided a guide to help you to understand what pressure your boiler should be, as well as how to fix your boiler if the pressure is too low or too high. Thankfully, diagnosing boiler pressure issues can be relatively simple and often easily fixed yourself.

Your boiler needs to have the right amount of pressure to circulate hot water and warm up your home effectively, so if your boiler pressure keeps dropping or is too high, it’s likely to cause a problem. 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 is off. An unbalanced water to air ratio can result in the system becoming over pressurised and possibly result in a breakdown.

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 to be sure your setting is correct. The optimal boiler pressure for a Worcester Bosch boiler is 1.5 bar.

You can also check your current boiler pressure by looking at the built-in boiler pressure gauge needle, which is usually highlighted in green. 

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

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

However, if the pressure relief valve itself is faulty or broken then we’d strongly recommend you call a Gas Safe engineer. 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 pressure 
2. Your system is above the correct pressure and your pressure relief valves have not released
3. The pressure relief valve has a leak and 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 a Gas Safe engineer to check the problem. 

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 yourself, we suggest you call a Gas Safe engineer out to examine it.

You can bleed water from your radiators, but if you don't feel confident in doing this, we recommend you call a Gas Safe registered engineer to look at your system.

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.

There are two methods of topping up your boiler pressure, depending on the type of boiler that you own and also which option your installer may have chosen for you. Watch the video below for advice on repressurising your boiler.

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. 

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.

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

If you have tried these fixes but you still have a problem 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.