Why does the boiler pressure matter?

Most central heating systems are closed. This means that there are no open vents to accommodate the expansion and contraction of water as it heats and cools. Instead, the system is sealed and pressurised to make up for these changes. The pressure is crucial to your heating operating properly.

Most boilers have a way of detecting if the pressure is off. They will cut out when the pressure falls too low and some models do the same when the pressure is too high. So if the pressure is too low, your boiler will turn off and you won’t have any hot water. Alternatively, high boiler pressure puts unnecessary strain and the system could break down.

What pressure should my boiler be?

Generally, your boiler pressure should be between 1 and 2 bar. However, read your boiler’s manual or ask your heating engineer for the required pressure for your particular model.

To check your boiler’s pressure, you need to locate the pressure gauge on your boiler. If there is the correct amount of pressure in your system, the needle should be between 1 and 2 bar. This area is usually designated in green. Below 1 and greater than 2 is in red, indicating critical zones.

Some boilers have a pressure gauge with 2 needles—the red needle serves as a marker while the black one shows the actual pressure. If the system has the right amount of pressure, the 2 should be pointing to the same number. Other boiler models have an LCD display showing the water pressure.

What if my boiler pressure is too low?

If the boiler pressure falls below 1, you’ll need to top up your system. The steps to do this will vary according to the specific boiler model so consult your boiler’s instructions. However, in general, you’ll be doing the following:

• Turn off your boiler and wait for the system to cool.
• Use the filling link or loop. There are 3 types:
  • External: Attach the filling loop to the corresponding valves and slowly move the lever. Keep doing so until the pressure needle moves into the green zone. Disconnect the external filling loop.
  • Keyed filling link: Insert the internal filling key into the loop and twist until it is closed. Turn the nearby knob so that water starts filling into the heating system. Do this until the pressure needle moves into the green zone. Turn the knob back to its original position and remove the key.
  • Keyless filling link: Simply move the filling lever until you hear water entering the heating system. Keep the lever lifted until the pressure needle moves into the green zone. Release the lever.
• Turn on your boiler and check to see if the pressure holds.

If after all this, you still find that the pressure falls below the recommended amount, there could be a problem with the gauge or with your heating system. At this point, you’ll need to call a registered heating engineer to inspect and service your central heating system.

What if my boiler pressure is too high?

If the boiler pressure is above 2 bar or the needle is in the red zone, you’ll need to release some of that pressure. The best and easiest way to do this is to bleed 1 or a few of the radiators in your home.

• Turn off your heating system.
• Place a radiator key or flathead screwdriver into the top valve. Turn the valve anticlockwise.
• At first, air will escape. After that, water will start to flow out of the valve. Catch the water in a small bowl or absorbent rag.
• Keep an eye on the pressure gauge while you do this. Keep the valve until the pressure needle falls back down into the green zone or between 1 and 2 bar.
• Close the valve.

When should I check my boiler’s pressure?

Usually, the pressure should remain relatively stable so you don’t need to check it every day or week. Instead, it is a good idea to check on your system’s pressure at least once a month.

If the heating season has just begun, then check your boiler pressure to ensure that it will work properly for the upcoming winter months. Also, if you bleed any radiators, check the boiler pressure to make sure that it hasn’t fallen too much.

Need help regarding your boiler’s pressure?

Then don’t be afraid to contact a professional heating engineer! Get in touch with up to 6 heating companies at once to easily compare their profiles, services, and prices. You are able to ask any question you have about your boiler’s pressure and get a second (or third, or fourth, etc.) opinion. You’ll get the best information on how to maintain your heating system properly!