What should my boiler pressure be?

How to guides

There are many reasons why you suddenly don’t have any hot water or heating, but a common problem is irregular boiler pressure. Luckily, this is often a quick and easy fix that doesn’t always require a call out from an engineer. Read on for more information about boiler pressure and how to fix related problems yourself.

What is boiler pressure?

Your gas boiler heats cold water and pumps it around your home through your pipes and radiators. For it to work efficiently, the water needs to be pressurised and stable. Drops and rises in pressure can cause a variety of problems to your central heating system, and will usually leave you with no hot water.

What should my boiler pressure be?

On the front of your boiler, you should find a gauge ranging from 0-4; this is the pressure gauge. Some boilers are colour coded to show low and high pressure zones in red. Normal pressure is indicated by the green zone.

What should my boiler pressure be when in use?

When the heating is on, normal boiler pressure should be around 2 - 2.5. If it rises above 3, there is cause for concern. Bleeding your radiators may help to reduce the pressure but if this doesn’t work, there may be internal problems to which you’ll need a Gas Safe engineer to take a look at it. Don’t be tempted to take a look inside your boiler; this can be quite dangerous and should only be undertaken by a qualified engineer.

What should my boiler pressure be when not in use?

When the heating is not in use, normal boiler pressure should be around 1 - 2. If the pressure drops below 1, your boiler has too little pressure and may have a leak. Try repressurising your boiler, but if the problem persists, it’s time to call out an engineer.

Why is my boiler pressure too high?

There are various reasons why your boiler pressure is too high. Most commonly, high pressure is caused by repressurising a low-pressure boiler, letting in too much water. Alternatively high boiler pressure could be due to internal parts not working correctly, notably the pressure release valve.

Small increases in boiler pressure is completely normal, particularly if your boiler is active, however your boiler can sometimes become over pressurised. High boiler pressure is usually not dangerous, and a working pressure release valve should control the problem. If worst comes to worst, the boiler should turn itself off if the pressure rises too far above normal.

Why is my boiler pressure too low?

Unless you regularly check your boiler’s pressure gauge, you may not notice that the pressure has dropped until you suddenly don’t have any heating or hot water. There are two common causes of low boiler pressure; boiler leaks, and bleeding your radiators.

Bleeding radiators takes water out of the central heating system, and will therefore lower boiler pressure. Similarly, leaks, no matter how small, result in your boiler losing water and pressure. Don’t be tempted to take a look inside your boiler to check for leaks as this can be dangerous. Make sure to call out a Gas Safe engineer to do this.

How to repressurise your boiler

If your boiler pressure is too low, you’ll need to repressurise your boiler (unless you spot an obvious leak, in which case you’ll need to contact a Gas Safe engineer).

Before attempting to repressurise your boiler following our instructions below, consult your boiler’s manual, as systems can differ. If you don’t have a manual, check your brand’s website.

  1. Turn off your boiler and allow it to cool.

  2. Find the filling loops, or attach it to the boiler.

  3. Ensure that you can still see the pressure gauge whilst using the filling loop. If not, ask someone to help.

  4. Open the valves to let cold water into the system.

  5. When the pressure gauge reaches 1.5, close the valves.

  6. Turn the boiler back on and press the reset button if needed.

  7. If the filling loop is an attachment, don’t forget to remove it, being careful in case there is water inside it.

What to do if your boiler pressure is too high

As with low boiler pressure, you might find yourself with no hot water or heating as a result of high boiler pressure. In this situation, try bleeding your radiators to remove excess water in the system. If the problem persists, your boiler may be faulty in some way and you’ll need to contact a Gas Safe engineer.

Scott Flannigan

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