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How to reduce or increase your boiler pressure

Boiler pressure optimum and recommended number

What pressure should my boiler be?

To run efficiently your boiler must have the right pressure to properly circulate hot water around your home. For most boilers, the correct pressure should be between 1 and 2 bars.

To check the pressure, your boiler will have a pressure gauge with a needle that is pointing between 0 to 4. The recommended pressure is between 1-2 bars and this is often marked as a green area on the meter. If your boiler has an LCD screen, the pressure will be shown when you click through the various options on the screen. 

Boiler pressure too high needs to be lowered

How should I lower my boiler pressure?

If the pressure in your system is too high, you’ll need to bleed your radiators. This is a common occurrence for un-vented heating systems and can cause cold spots in your radiators.

Bleeding your radiators will reduce the pressure in your central heating system and boiler - you’ll need to keep bleeding the radiators until the pressure gauge returns to a safe level.

Steps to lowering your boiler pressure

Before you get started, you’ll need a radiator bleed key and some tissues, or a hand towel, to catch any drips. 

  1. Turn your heating on – this will warm up your radiators and build pressure in your system.

  2. Check your radiators – if you can hear gurgling sounds and your radiators have cold spots, you’ll need to bleed those specific radiators.

  3. Turn your heating off – if you don’t, you’ll be at risk of scalding yourself and getting hot water on the floor.

  4. Get the tissues ready – when you bleed a radiator, some discoloured water will come out and will need to be caught before falling on your carpet/floor.

  5. Open the radiator bleed valve – using your radiator bleed key, insert it into your bleed valve, this is often found at the side of a radiator and looks like a round hole with a square inside. When you insert the key, you’ll feel them lock together, turn the valve anti-clockwise – you’ll hear a hissing noise which is the hot air escaping, so be careful.

  6. Bleed your radiator – a quarter-turn of the valve will be enough; don’t turn it too far or else water will come rushing out. Hold the radiator valve open until the air stops coming out and water starts to drip out - this means you’ve successfully bled a radiator.

  7. Seal the valve – turn the radiator bleed valve clockwise to tighten, making sure not to overtighten. Repeat the above processes on all the radiators that need bleeding.

  8. Check the pressure on your boiler – once you’ve bled your radiators, check your boiler’s pressure gauge to see if your system needs to be re-pressurised. If it’s between 1.0 - 1.5 bars then you’re all done. 

  9. Adjust boiler pressure - if your boiler pressure is too low then you need to manually increase the boiler pressure, this could be with a central filling loop that’s connected to your boiler, or some valves you may have to open underneath the boiler. Find out what make and model your boiler is, then go to the manufacturers' website, they'll have a walkthrough video/blog about how to increase it for your exact boiler. 

Your boiler pressure should now be back to the recommended levels.

Increase boiler pressure for your boiler how to increase boiler pressure

How should I increase my boiler pressure?

If you're having issues with your boiler and get a loss of water error code, it's likely you have low boiler pressure.

If your water pressure is too low it won’t cause any damage, but it will affect the efficiency & effectiveness of your boiler – so you’ll be paying more in energy bills.

The standard operating pressure is usually 1 – 2 bars of pressure. Anything above or below that will need to be repressured. 

This is an easy issue to fix and you can even do it without getting an engineer to your home. We've listed the most common way to increase boiler pressure for the majority of boilers below. 

How to increase boiler pressure

Each boiler is different and will have different ways to increase the pressure, so it's very important to find out which boiler make and model you have. When you know it, proceed to the manufacturer's website and they'll likely have a blog/video that will explain how to increase your exact boiler's pressure. 

Here's the most common way to increase boiler pressure:

  • Switch your boiler off and let it completely cool.
  • Find your boilers filling loop. This is a flexible hose found underneath your boiler with a small valve at each end, make sure both ends of the hose are secured and attached to the two valves.
  • Use the valves handles on either side, turn them clockwise and open the valves. This will then allow the cold mains water into the system, and you'll hear it filling up the system.
  • The pressure will now increase, so pay attention to the pressure gauge until it gets to the 1.5 bar mark. You'll then want to start closing both valves by turning the valves counterclockwise.
  • Turn the boiler back on and reset your boiler if necessary.