What should boiler pressure be?

17 January 2023
What should boiler pressure be?

What should boiler pressure be?

A boiler pressure gauge reading 1.5A boiler pressure gauge reading 1.5

The water inside central heating systems needs to be able to travel around the network of pipes and radiators in a home. Often this means going against the force of gravity, such as in a two-story home, so there needs to be a certain pressure inside your system to ensure the hot water gets where it needs to. If the boiler pressure is too high, leaks could form in your central heating. If the pressure is too low, water won't flow correctly around your system. The right boiler pressure will allow your system to be running effectively and efficiently.

What should boiler pressure be when the heating is on and off?

Boiler pressure is measured in bars and a healthy boiler pressure should be somewhere between 1 and 2 bars. You can check your boiler pressure by looking at the gauge on your boiler.

  • When the heating is on, you should see your boiler pressure rise to between 1½ and 2.
  • When the heating is off, or cooling down, you should see your boiler pressure lower to between 1 and 1½.

How to increase boiler pressure

Some common signs that you've got low boiler pressure are:

  • Your radiators won't get hot
  • You've got no hot water
  • The gauge on your boiler has dropped below 1

A drop in boiler pressure could be due to a small water leak, which obviously needs investigating, or as a result of bleeding your radiators. Fortunately, re-pressurising your heating system is not too difficult provided you follow the instructions below.

1. Switch off your boiler and allow your heating system to cool down

2. Find your filling loop, which is normally located under your boiler. If it isn't, look in your boiler's manual to try and work out where it is.

3. At the filling loop, you will see two pipes with valves or handles. With an eye on your boiler's pressure gauge, open up these valves to allow water into the system.

4. You should notice your boiler pressure increase and can turn off both valves when the pressure reaches 1½ (halfway between 1 and 2 bars).

5. Wait a few minutes and see if your boiler pressure stays between 1 and 2 bars on the gauge. Also have a quick look around your radiators and pipes to check for any leaks.

6. If everything looks good then switch your boiler on again and check that your radiators are getting hot.

7. After using your heating, turn your boiler off again and check that the pressure hasn't dropped again.

How to reduce boiler pressure

Some common signs that you've got high boiler pressure are

  • The needle on your pressure gauge has increased dramatically or gone into the red
  • Your central heating system has completely shut down

High boiler pressure is not a problem that happens too often, but if it does, it could have been caused by the valves on your filling loop being left open, allowing water to continue to flow in your system. Additionally, high boiler pressure is often a symptom of trying to correct low water pressure, whereby too much water is allowed in at the filling loop in an effort to boost boiler pressure. Whatever the reason, high boiler pressure is rarely cause for concern because modern boilers have a pressure release valve that allows the excess water to escape. Boilers and heating systems will also shut down if they detect high levels of pressure.

In order to reduce your boiler pressure, try the steps laid out below:

1. Switch off your boiler and allow the system to cool down

2. Locate your filling loop and close the valves

3. Take a radiator key and bleed each radiator in your home. You'll hear air escaping as the pressure is relieved but have a cloth on hand to catch and drips.

4. After bleeding each radiator, check your pressure gauge on your boiler to see if it has lowered. If not, repeat the process of bleeding your radiators again until the pressure drops to below 1 and 2 bar, or at least comes out of the red zone. If your boiler pressure won't come down having carried out these steps then call in a professional to diagnose the problem.


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