What to do if your boiler pressure is too low

Most UK households use a gas combi boiler for heating and hot water, with a pressure gauge that can usually be located on the control panel. It is usually a circular dial and may have green and red zones marked on it. The green zone is the standard operating pressure and is usually between 1 - 1.5 bar. The red zone indicates the maximum safe operating pressure.

If your pressure gauge is marked with a green zone and the needle has fallen below it, this is a sign that the gas boiler pressure is too low and action should be taken.

If you have radiators that fail to heat up as they should, this may also be a sign that there is an issue with your boiler pressure and can be confirmed by checking the gauge.

It is not always easy to find a water leak in your system as there will often be pipework that is not visible. However, it if you are experiencing low boiler pressure then it is worth conducting a visual examination of the pipes and radiators that are accessible. Look for any water on the pipework, as well as other signs of moisture such as damp patches or stains, and sometimes swelling in the skirting board. Copper pipes may also develop a green build up over time if moisture is escaping. Joints in the pipework are a common place to find leaks, as are the points where the pipes are connected to the radiator. Be careful not to mistake condensation for a leak, especially in colder rooms.

If you have inspected all visible pipework and have not identified any leaks, you may need to contact a Gas Safe registered engineer to check inside the boiler itself.

The most effective way to fix a problem with low boiler pressure is to repressurise the system. This can usually be done yourself without the need to call a Gas Safe engineer, but you should always check the user guide first to ensure that your model allows this.

If it is safe to repressurise your boiler yourself and you feel confident to do so, this can be done by following these simple steps:

1. Identify your filling-loop and pressure gauge. The filling loop handles should be at a 90° angle to the flow of the pipe.
2. Make sure that you can see the pressure gauge whilst accessing the filling loop. The correct pressure level will often be shown in green on the gauge for modern systems, however you should check the pressure for your specific model in the manual prior to beginning the procedure. It may be a good idea to get someone to help you.
3. Turn off the boiler.
4. Turn both filling loop handles at a right angle, so that they match the direction of the pipe. You should now be able to hear water flowing.
5. Once the correct pressure is reached, make sure the handles are fully closed by returning them to the 90° position.
6. Turn the boiler back on and check if the pressure remains steady.

If you have followed these steps and your boiler maintains the correct pressure, then you can relax in the knowledge that everything is back in order.

Should the pressure drops again then this is a sign that something else may be wrong and it is advisable to contact a service engineer.