How to check the boiler pressure

As boiler pressure is the most common reason for a boiler breakdown, it is essential to check your boiler pressure. On most modern combi boilers, the pressure gauge can be found either on the front of the boiler or under the control panel. If your boiler is older, the pressure gauge might be located near the pipework. You can use your instruction manual if you are unsure where your pressure gauge is located.

It is useful to do a monthly check of your boiler to identify any obvious issues and to check that your boiler’s pressure is perfect. Boiler pressure may also be brought up during an annual service, so the specialist may fix it on your behalf and identify the cause of the issue. To find out the importance of annually servicing your boiler, please click here.

Standard boiler pressure

Standard boiler pressure is between 1 to 2 bars. Fortunately, most pressure gauges can show you if the pressure is perfect by using red and green sections. The green section means the boiler pressure is fine and doesn’t need changing. If it is in either of the red sections, it means the pressure is either too high or too low. Please be aware that your boiler may still continue to work, even if the pressure is too high or low, so it is important to check and adjust the pressure when necessary.

High boiler pressure

High boiler pressure is not always a serious issue; most boilers have mechanisms to counteract high pressure. Many boilers will shut down if the pressure is too high, or the valve may release some water into a small pipe away from the boiler to resolve the issue.

Signs of high boiler pressure

Unlike low boiler pressure, there are only two simple signs to look out for. If the system has shut down, or the gauge is in the red section, then the boiler pressure is high.

Causes of high boiler pressure

High boiler pressure is usually accidentally caused when adjusting boiler pressure. Sometimes, when fixing low boiler pressure, it might be adjusted too much and cause higher pressure than intended. In addition to this, if a valve is not tightened enough, this can cause too much water to flow, which can impact the pressure. If this is the case, you will need to tighten all valves to stop the overflowing of water.

If your boiler has high pressure and it was not caused by adjusting pressure or by having loose valves, then it is likely that your boiler is faulty, and may need checking for issues.

How to reduce high boiler pressure

In most cases, it is possible to reduce high boiler pressure without needing to contact a boiler specialist. If you follow these steps, but it continues to increase, then you should contact us for further guidance as it could be caused by a faulty boiler.

Step 1: Turn off your boiler
Step 2: Make sure all valves are tightened
Step 3: Once the system has cooled down, bleed your radiators. If you have any issues with bleeding your radiators, contact a professional immediately – it is very easy to bleed a radiator incorrectly!
Step 4: Check the pressure gauge. If the pressure is still high, bleed your radiators again

Low boiler pressure

Low boiler pressure is usually more noticeable than high boiler pressure due to the effects low boiler pressure has on heating the building. On Average, a boiler will need the pressure increasing between every 6 months to 12 months due to the heating system naturally heating and cooling water.

Signs of low boiler pressure

Low boiler pressure can cause no heating or hot water to go around the system due to there not being enough pressure in the system. If you notice these issues, you should check the gauge on your boiler (usually located on the front, on the front panel, or on the pipeline).

Another sign of low boiler pressure is the gauge showing the pressure in the red section. If it is only slightly low, you may not lose hot water or heating to a noticeable degree, so it is useful to check your boiler pressure from time to time to make sure it is not too high or low.

Causes of low boiler pressure

There are three main causes of low boiler pressure:
Water heating and cooling: Naturally, boilers will lose pressure over time due to water heating and cooling within the system. As a result of this, you may need to repressurise your heating system every 6 months – 12 months. If this is the case, this does not mean that your boiler is broken or there are any issues within the heating system, so there is no need to panic.
Small leaks: Sometimes, a leak may occur in the pipelines. These leaks can be so small that you may not notice any water escaping, but over time, the water escaping will build up and cause the pressure to decrease.
Bleeding your radiators: As water can escape when bleeding your radiators, it can slightly decrease the pressure

If you have high boiler pressure and reduce the pressure, you can also cause the boiler pressure to be too low. This is not a common cause of low boiler pressure but can be easily fixed.

How to increase low boiler pressure

Increasing your boiler’s pressure is a simple task and can be done without the help of a professional. By following these steps, you can repressurise your heating system:

Step 1: Turn off your boiler
Step 2: Locate either the filling loop or the keyed filling loop, depending on the type of boiler. The filling loop is a hose that connects to two water pipes, with two levers to control the valves. If you cannot find your filling loop, you should refer to the boiler manual.
Step 3: Turn both levers so they are aligned with the direction of the hose. If this is done correctly, you should hear water starting to run.
Step 4: Keep an eye on the gauge and stop the valves once the gauge hits roughly 1.2 bar. Make sure that both valves are closed to avoid high boiler pressure.

Top tip: Do not turn on your boiler straight away, you should wait before using it to check if the pressure is still decreasing. If the pressure continues to decrease, you should look for leaks. You should contact a boiler specialist if you suspect a leak, in order to amend it and receive the most appropriate recommendations for your specific heating system.

If you would like to learn more details about low boiler pressure, read our guide to low boiler pressure here.

In conclusion, usually boiler pressure being too high or too low is not a big problem. As you can adjust your boiler’s pressure, you can fix most pressure issues without the worry of having to call a boiler specialist. However, you should contact a boiler specialist if you have any concerns with adjusting your boiler pressure or you are still having issues after adjusting the pressure.

If you have any boiler concerns or would like a boiler installed, please do not hesitate to contact us at or 1274 317169.