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31st January 2018
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How to fix your boiler pressure: bleeding and filling

white boiler on a wall in the home


Moving into your new home can be exciting (and stressful!), but before you can think about decorating your new space and getting inspired by pretty Pinterest posts, it’s important to take time to understand your home maintenance first. One of the most important things on the list is your boiler, and the sooner you check it the better. If you find that there is a fault, you could be left without proper heating for hours or even days or weeks. While many boiler issues are complex, a few more simple issues can be put right with patience and the correct guidance.

Boiler pressure vs. Water pressure

Your boiler is the central nervous system of your home. It moderates your central heating and water, and it’s important to remember that the boiler pressure is different to water pressure. Your boiler pressure is the pressure of the hot running water in your closed central heating system; your water pressure is the pressure of water running when you turn your taps on.

pressure gauge indicator at 1.2 bar

How to check the pressure of a boiler

To check whether your boiler is operating within the correct limits you should you should first consult the pressure gauge which is usually found on the front of the control panel or the tank of the boiler. While not every boiler has the same pressure requirements, most central heating systems perform within the 1 – 2 bar.

Is my boiler pressure too low?

If it is at 1 or below, this probably means that you will need to repressurise your boiler as when your boiler pressure is too low, your system can cut out and leave you with no central heating running through your home.

How do I know if my boiler pressure is too high?

If your boiler pressure is approaching or exceeding around 3 bar you may need to consider reducing it. If your pressure is too high it can over-strain the system, potentially causing it to fail, and again leave you with no heating until it is professionally repaired.

Even though boilers come in all shapes and sizes (from conventional to combination) the repressurising and depressurising process is usually relatively similar. You can find our handy tips below:

Low Pressure: How to raise the pressure of a boiler


If your boiler pressure is below 1 on the gauge and you’re worried about having to spend a cold night without central heating, here’s what to do:

  1. The first thing to do is to switch off the boiler system and let it cool. This will reduce the pressure in the system and prevent you being burnt by any of the boiling water in the system.
  2. Once cooled, you will need to locate your filling loop. This is a flexible silver/grey hose with small valve attachments at each end.
  3. One of these valves is connected to your cold water system. This valve can then be opened with a tap to allow the mains water to go the filling loop and into the system.
  4. At this point, you should hear water filling the system.
  5. Always keep a close eye on the pressure gauge while filling so that when it reaches the optimum pressure bar between 1 and 2 you can turn off both valves one after the other.

If the pressure still falls below 1, then this means there is a fault with your boiler system or the gauge. Unfortunately meaning you will have to contact an engineer.

High pressure: How to reduce the pressure in your boiler

Hand turning key to bleed radiator pressure

As previously mentioned, If you pressure gauge reading is exceeding 3, then the pressure is likely to be too high, over-straining the system and causing it to potentially fail. In this case, you will have to bleed your radiators. Here are a few tips to help you:

  • To relieve the pressure in your central heating system once again the first thing to do is to turn off your boiler and let your system cool.You’ll need your radiator key or a flat-head screwdriver that’s a similar size to the slot for the key. You’ll also need a shallow bowl to put under the valves that you’re bleeding, and a towel to prevent the stream from damaging your walls.
  • You should always start by bleeding the downstairs radiators before bleeding the ones on higher levels.
  1. Firstly, open the valve with the key by turning it anticlockwise.
  2. When it’s open, you will hear air escape, be sure to have the towel on hand so your walls do not get damaged when the water begins to flow through.
  3. When water starts to bleed out, catch this with the shallow bowl.
  4. Keep an eye on the pressure gauge or get someone to watch it whilst bleeding, get them to shout to you when you have reached the optimum pressure so you can stop the bleeding process.
  5. Modern radiators can have water coming through as a jet rather than a drip bleed so please be cautious of this and have all the necessary protection like bowls/towels etc.

If your pressure gauge isn’t changing whilst bleeding your radiator, then it may be broken. At this point don’t hesitate to contact an experienced engineer.

Hopefully, with our advice, you were able to successfully repressurise or repressurise your boiler. If you’re having any further issues feel free to get in touch.

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