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What Should My Combi Boiler Pressure Be?

Combi Boiler Pressure

One of the most common questions that our team receive from our clients in Cardiff, is what pressure should their combi boiler be on? Your combi boiler pressure should be between 1.0 and 2.0 bar for perfect operating conditions. This can be confirmed by Baxi, who are one of the biggest boiler manufacturers in the UK.

A boiler losing pressure can be a result of the following issues:

  • Boiler is leaking
  • Faulty pressure release valve
  • Faulty pump speed
  • … and more.

A boiler that has a high pressure is usually the result of the water that has expanded during the heating process. Once you have finished using the central heating system or running hot water, the pressure should return to normal levels. If this is not the case, you may have an issue with the pressure relief valve that controls this process.

It is more common for your boiler to have a lower pressure than a higher one. The combi boiler pressure can be easily reset as shown below.

How To Increase Boiler Pressure

In order to increase the combi boiler pressure, we advise that the boiler is off and cooled down. Underneath the boiler, there will be a flexible hose with a small valve at each end. Depending upon the boiler brand, you can use a flat headed screw driver or simply spin the valve.

By doing this, you will be adding cold mains water into the system, which you will be able to heard whilst filling the system. As you do this, be sure you are checking the gauge and aim to finish refilling the system at 1.5 bar.

increase boiler pressure

How To Lower Boiler Pressure

The first thing you will want to do is ensure that the pressure relief valve is tightly closed and not accidentally left open. This can be easily forgotten and if left, will constantly add water into the boiler.

To reduce the pressure in your boiler (and central heating system), we advise that you bleed the radiators until the boiler is reading between the recommended pressure.

If the boiler is continuing to read high levels of pressure, there may be a fault with the filling loop of the expansion vessel requires re-pressurizing. Both of these will require a Gas Safe Boiler Engineer to fix and confirm that it is safe to use.


Checking the combi boiler pressure on a regular basis is highly recommended. Failing to do so may cause stress upon your central heating system as well as inefficiency. If you have any troubles with your combi boiler pressure, feel free to get in touch with our team.

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180 Ffordd James McGhan, Cardiff, CF11 7JU
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