What Pressure Should My Boiler Be On?

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What Pressure Should My Boiler Be On?

Your boiler is a workhorse. It quietly (hopefully) gets on and does a sterling job providing hot water and heating, without you needing to give it too much attention. However, one element you do need to be aware of is the boiler’s pressure. Knowing the answer to ‘what should boiler pressure be when heating is on?’, or knowing when boiler pressure is too high, is vital to spotting problems early.

It’s a Pressure Problem

Boilers aren’t happy when the pressure is either too low or too high. However, when it is too high, this is a particular problem. Low pressure can also be a sign of a leak somewhere in your system.

It doesn’t actually matter which type of boiler you have, the operating pressure of all combi boilers is very similar. Therefore, whether it is Bosch, Valliant, or a different brand, you need to understand the basics of pressure. Nonetheless, you should refer to your boiler’s manual to see the optimal pressure gauge readings for your particular boiler.

The pressure gauge is usually located underneath your boiler, or on the boiler itself towards the bottom. It looks like a dial and typically will have numbers between 1 and 5.

As the Boiler Changes Heat

When your boiler is cold, you should usually expect the pressure reading to be between 1 and 1.5.

When it comes to knowing what boiler pressure should be when heating is on, it is important to note that it is normal, and ok, for the pressure to rise from this optimal cold number.

However, you shouldn’t anticipate big changes in the pressure gauge. As the boiler is working, heating up water, the pressure does go up, but only slightly. You shouldn’t see a jump of more than 0.5 bars. If the number is rising more than this the boiler pressure could be too high.


The rising pressure when the boiler is working is simply down to the heat expanding the water in the system. Being a closed system, it just means the pressure goes up slightly as the hot water travels around from radiators and pipes.

Typical Boiler Problems When Pressure is Too High

When boiler pressure is too high, this can be an indication that there is a problem with the release valve or the expansion vessel. It’s best to get these investigated as soon as possible before they become major problems. You can find out more about our boiler breakdown service here.

It may also simply be that you’ve manually increased the pressure too much. If this is the case, bleed a radiator, such as a towel rail, and release some of the pressure. Keep checking the gauge until it drops back down to optimal range.

Conversely, if the pressure is too low, this can also indicate a problem. In the first instance, you can try increasing the pressure of the system. You can do this manually by opening the pressure valve and letting more water into the system. This should be explained within your boiler manual.

Generally, you shouldn’t need to do this more than once or twice a year. If your boiler is more regularly losing pressure, then there is likely a more concerning problem, such as a leak.

If the boiler’s pressure gauge keeps dropping, despite you adding water to the system, you will need to get the system investigated for leaks.

Problems with Your Boiler’s Pressure

If you are repeatedly having problems with your boiler’s pressure then it is an indication that something’s not quite right. Get in touch with us on 0333 939 0161, and we can come and see what the problem is.

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