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09 Jul 2019

What is the ideal pressure for a boiler?

By Oliver
  • Read time: 2 minutes
Water and radiators are heated by pumping boilers pushing hot water throughout a series of pipes within your central heating system. For this to happen, however, the boiler pressure level must be just right.

What is the correct boiler pressure?

There are many different boiler models, each with different pressure settings. There can’t simply be one set pressure which fits all models. Generally speaking, the ideal pressure for a boiler is between 1 and 2 bars as most households are fitted with a low-pressure boiler. The boiler pressure gauge can be found on the front of the boiler; a small needle will point to the pressure setting, often on green and red sections to notify you of the level of risk.

If your boiler pressure is too high, the needle will point towards the red section of the gauge, or over 2 bars. A boiler running at high pressure can lead to failures within the central heating system or even damage your home if pipes burst. Should your boiler pressure be too low (drops below 1 bar), the central heating system will shut off leaving you without heating and hot water.

How to re-pressurise a boiler

Typically, to lower the pressure of your boiler, you need to bleed one or more radiators. If you’ve noticed some radiators aren’t heating up properly – maybe they are cold towards the top, or in the middle – there is too much air in the system which needs to be released. 

If you’ve bled the radiators but the boiler continues to show it is working at a high pressure, you will need to contact a Gas Safe Engineer and have them inspect the boiler.

On the other side of the scale, if the pressure is too low – it needs topping up. A simple process, the filling taps should be opened to release enough pressure into the system before closing again.

The boiler pressure keeps dropping

You might ask – ‘why does the pressure read lower at certain times of the day?’ Well, the simple answer is because the boiler probably isn’t working. When a boiler is on and working to heat your water or radiators, the pressure will be closer to 2 bars as the water within the pipes becomes hotter and expands. So naturally, when the boiler isn’t on, the pipes are cooler which causes a slight drop in pressure. This isn’t anything to panic about – it is normal.

While you don’t need to check the pressure on your boiler every day, there are a few key times you should check in:

After summer: As autumn and winter approach, your boiler will begin to work harder than it has for a while. You need to make sure it is up to meeting the high demands, starting with the pressure

After bleeding a radiator: If you’ve had to bleed one or more radiators throughout your home, you will need to check the pressure hasn’t dropped too low or you might have to top it up

Boiler pressure dropping: If the pressure is lost on a regular basis, (below 1 bar), you may need to speak to a Gas Safe Engineer as you could have a leak within the system. Better to catch the leak early, to prevent further (and potentially more expensive) issues down the line.

If you ever struggle to understand topping up or lowering the pressure of your boiler, or if any other issues arise, contact a Gas Safe Engineer who can assist you.


Written by Oliver

Oliver is a Content Specialist for 50five UK