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What pressure should my boiler be?

people gathered around boiler in kitchen

What you'll learn

  • What pressure should my boiler be when the heating is on?
  • What pressure should my boiler be when the heating is off?
  • Why does my boiler pressure rise when the heating is on?
  • What do I do if my boiler pressure is too high?
  • What do I do if my boiler pressure is too low?

What pressure should my boiler be when the heating is on?

A boiler’s pressure gauge will usually sit between 1 and 2 bars when it is turned on. The exact recommended pressure level will vary depending on the boiler manufacturer, but generally, anywhere between 1.0 and 2.0 bar is ideal.

The boiler pressure level will rise when heating a home or providing hot water. However, it should still stay below the upper-pressure limit of 3 bar. Always check your boiler manual to see what the recommended boiler pressure level is for your boiler.

What pressure should my boiler be when the heating is off?

Boiler pressure should generally be between 1 and 1.5 bars when central heating is turned off. The needle of the pressure gauge should remain above the lower limit set by your boiler manufacturer at all times. Always check your boiler manual to see what the specific recommendations are for your boiler model, as this varies depending on the manufacturer.

installer checking radiator

Why does my boiler pressure rise when the heating is on?

When water is heated, it expands. As the boiler heats the water within the central heating system, the increased temperature causes the hot water to expand, this results in a pressure rise. The rise in pressure can be identified from either a digital or mechanical pressure gauge on or in the appliance.

This is completely normal and should not be a cause for concern; even if the pressure continues rising above the upper limit for the boiler model, all appliances are fitted with safety controls to compensate for the increase.

What do I do if my boiler pressure is too high? There are three possible reasons why your boiler pressure is too high:

  • Too much pressure

    If you have recently topped your system pressure and accidentally added too much pressure. There is no need to panic as this is quite common, you have a couple of options now: (a) If the pressure at room temperature is less than 2.5 bar, no action is required, however bleeding a couple of radiators will reduce the pressure. (b) If the pressure is greater than 2.5 bar, reducing the pressure before operating appliance is advised. Again, this can be done by bleeding a radiator or seeking assistance from your installer or a local plumber.

  • External filling device is faulty

    Your external filling device is faulty (a pressure filling device not located on the appliance, usually under the appliance on the pipework) These devices may not be fully closed or could be allowing water to pass through a closed valve. This results in a continuous pressure rise.

  • Faulty boiler

    Your boiler could be faulty, over time the parts inside the boiler can begin to malfunction, especially if it has not been serviced regularly by a Gas Safe registered engineer. If you have bled your radiators and the boiler pressure is still too high you should call a qualified engineer to inspect your appliance/system.

What do I do if my boiler pressure is too low?

If your system pressure is low it means there is not enough water in the system. This is usually because of a leak, which most commonly occurs around the plumbing fixtures. Check for damp spots or rust marks around your radiators, as well as flaking wallpaper.

If you have found the source of the leak, a competent person can easily repair it. Once the leak has been fixed, you can repressurise the boiler using the system filling loop. This location of this device varies depending on the boiler model, so check your boiler manual to see what type of filling loop you have.

If you have not found a leak, it may be that your boiler is faulty and you should call a Gas Safe registered engineer to inspect the system. Similarly, if you have fixed a leak and repressurised the system but the boiler pressure is still too low you should immediately close the filling loop and call a qualified engineer.

Summary

  • The normal level of pressure that a boiler operates at is between 1 and 2 bars. Check your boiler manual to find the recommended level for your model.
  • The boiler pressure will rise when it heats water in the system and drop slightly as it cools.
  • If your boiler pressure is too high, let your system cool and recheck the pressure. If the problem persists, contact a Gas Safe engineer to diagnose the problem.
  • If your boiler pressure is too low, you will need to increase the amount of water in the system by opening the filling loop valve, check your home for leaks if the pressure falls again or call a competent person.

Need more help? Contact your local installer

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