Skip to the content
Trustpilot logo 0800 61 22 302

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 and the needle will be between 1 and 2 bars, this is often be marked as a green area on the meter. On some boilers, with an LCD screen, the boiler pressure will be shown on the screen when you cycle through the various options. 

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 will reduce the pressure in your central heating system, which also lowers the pressure in your boiler. This is a common occurrence for un-vented heating systems and can cause cold spots in your radiators.

You’ll need to keep bleeding the radiator until the pressure gauge returns to a safe level.

Steps to lowering your boiler pressure:

Before you get started, you’ll need a cloth/towel (to catch any drips) and a radiator bleed key.

  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 cloth 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 of the air escaping, this could be hot, 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 until the air stops coming out when only water drips out, then 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 done - if it’s too low then continue to step 9.
  9. Adjust boiler pressure - locate the central filling loop that’s connected to your boiler, it looks like a tap and is connected to a mains water supply. Make sure to turn the tap slowly to adjust the pressure, if you put too much pressure in there’s also a bleed tap.

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

Whistling noises can be caused by kettling, loss of water or air is trapped within your system. If it is trapped air, you can easily fix this by bleeding your radiators.

If you don’t feel comfortable bleeding your radiators, you can always call a Gas Safe engineer to sort it out. When they bleed your radiators, they’ll also find out what caused air to become trapped in the boiler and perform the appropriate repairs.

There will be a call out charge of at least £50 - £60 per hour.

How to increase 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 – 1.5 bars of pressure. Anything above or below that will need to be repressured.