How to Check and Fix Your Boiler Pressure

boiler gas pressure gauge
  • 0.5-1
  • Beginner
  • 15-50
What You'll Need
A boiler pressure gauge
What You'll Need
A boiler pressure gauge

The boiler pressure in your home's boiler should maintain a constant level as the boiler heats water and keeps it warm. These building heating systems are strong and durable, lasting for many years if they are well maintained.

Damaged or broken parts on a boiler, however, can lead to carbon monoxide leaks and other bad effects. This deadly gas can cause serious injury and death.

One important maintenance step to prevent this from happening to your boiler is checking the boiler pressure levels. Doing this on a regular basis will keep your home warm and safe.

It will also save you money in the long run by preventing large issues from arising that need major, costly repairs, as well as ensuring that your boiler has a long life and will not need to be replaced prematurely.

Step 1 - Locate the Boiler Pressure Gauge

The first thing you will need to do with any type of maintenance or repair is to find where your boiler's boiler pressure gauge is located. All boilers have a gauge that indicates the pressure inside.

The gauge is generally found on the side of the boiler. This device will tell the homeowner if the pressure in the boiler is excessive or at normal levels. The gauge is unlikely to be at the back of the boiler or anywhere difficult to see.

Step 2 - Read the Boiler Pressure Gauge

The pressure gauge on smaller home boilers should maintain a level of twelve to fifteen pounds. In the event that the boiler pressure is too high, a release valve can be turned to lessen the pressure. You should check this frequently as it can alert you to any issues with your boiler.

woman reading gauge on boiler

Step 3 - Get Professional Assistance

If the pressure increases immediately after releasing the valve, a professional service person needs to be contacted regarding the situation. This can spell disaster for your boiler system if not dealt with quickly and by someone with the know how necessary to fix the boiler system.

Consider having the pressure regulator adjusted in order to keep the pressure in the boiler at a lower level. Read the owner's manual provided by the manufacturer of your boiler for the necessary information to adjust your pressure regulator.

Rising Levels

Several factors contribute to the efficiency of a boiler. All the heating system parts need to be in good working condition. Adequate fuel must be constantly available, whether powered by diesel, natural gas, or oil and the water tank must always have adequate water inside of it to work properly.

The temperature and pressure settings must also be correct. You may sometimes experience rising pressure in the system. Below are four possible causes and actions to take.

Boiler Expansion Vessels

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The boiler's expansion vessel can be found at the rear of the heating system. The expansion vessel regulates pressure rises in the system. It sometimes becomes necessary, however, to re-pressurize this vessel to prevent frequent rising pressure in the set-up.

To do so, start by turning off the boiler. Drain all water from the radiators, then use a bicycle pump or foot pump to pressurize the vessel to a bar level of 1 to 1.5. It is now time to refill the radiators.

Once it has been refilled, turn the system back on. It should now work properly without any pressure problems. If it does not, you can call in the pros or a different issue may be at play with your boiler.

blue and red boiler expansion tanks

Boiler Expansion Tanks

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An expansion tankk's purpose is to accommodate the expanding water levels in the system. A blockage in the pipe that leads into the expansion tank, however, can hinder the smooth flow of water and should be adjusted immediately.

Check the connecting pipe for any blockages. Dirt and debris may have accumulated with time. Clear the pipe and fit it back into the system.

Too much water in the expansion tank and too little air may also cause pressure to rise frequently. If the bottom of the tank does not feel hotter than the top, it indicates an excessive amount of water. You need to drain this water from the tank.

To drain the water from the tank, begin by turning the boiler off. Once it is off, you will need to close the water shutoff valve and allow the system to cool completely. Attach a hose to the combination valve on the expansion tank. The combination valve will release water from the system and allow air in.

You should drain 3 to 4 gallons of water from the tank. If your system is an older model, it is unlikely to have a combination valve. Simply close the valve between the expansion tank and boiler and then completely drain the tank.

It is now time to open the water supply valves and refill the system. Pressure should remain stable during subsequent use. The expansion tank may also have some defects. It is best to replace the tank if it appears damaged or worn out.

Air Lock

Occasionally, air may get trapped within the heating system of your boiler. Pockets of air can cause the pressure to rise, making this dangerous. To eliminate air pockets, you need to bleed your heating system. This will help to stabilize pressure.

To bleed the boiler system, you will need to start by obtaining a small key from a hardware shop. Explain that you need to bleed your boiler. Fit the key into the slot at the radiator. Slowly turn it to release pressure until you attain the desired level.

Make sure to keep an eye on the gauge, or have a helper do so, as you bleed the system so you know when the job is complete. Keeping an eye on the gauge will prevent you from releasing too much pressure and make the job easier all around.

Defective Valves

Sometimes, a valve in the system may be faulty. This can cause water to seep into the heating circuit. As a result, pressure will then keep rising beyond the recommended level.

The pressure relief valve will then open and begin to drip. You will need to replace the faulty valve to correct the situation. This will also stabilize pressure. If you do not feel comfortable doing so yourself, you may want to bring in a professional.

leaking boiler valve

What Affects Boiler Pressure?

After reading all this you may be wondering what affects boiler pressure. In reality, a few things do. The pressure release valve and the filling loop are both factors in boiler pressure.

While you can inspect both yourself, you will likely need to call in a professional to make repairs and thoroughly check these devices as they can be dangerous to work with if you do not know what you are doing.

As always, spending a little time and money now can prevent you from having to spend a ton of time and money down the road as bigger issues arise.

What Causes Boiler Pressure to Rise?

You may also wonder what causes boiler pressure to rise. Simply put, boiler pressure rises when your boiler temperature is rising. This happens when the boiler is using gas, oil, or whatever fuel source it is powered by, in order to heat water.

Rising boiler pressure is not necessarily a bad thing, as long as it stops. It should rise as water is being heated. This is not a sign of a faulty boiler.

The pressure should, however, stabilize and level off once the system is switched off and has had time to cool properly. If it does not do so, there is likely an issue with your boiler pressure.

Ideally, your boiler pressure should be between one and two bars on the gauge found on your boiler. Make sure the gauge needle is in the safe area and not in the red zone. The gauge needle should be on the outside of your boiler in a place that is easy to view.

Take a look every so often to ensure that your boiler is running as it should. If it is in the red zone, you have an issue and should try to determine and fix the culprit immediately. This may be something you can do on your own or something you will need to get professional help with.

hands lifting a boiler cover

Can Boiler Pressure Drop Without a Leak?

You may be wondering if your boiler pressure can drop without a leak. The answer is yes. A boiler can lose pressure without a leak even though a leak is the most common cause of a boiler losing pressure.

A leak can also be caused by a number of other issues, such as a pressure relief valve program, an expansion vessel problem, or from bleeding radiators.

No matter the culprit, a leak in your boiler is never a good thing and should be dealt with right away by following the above advice.

What Happens if Your Boiler Pressure Is Too High?

You may be wondering if your boiler pressure being too high is really that bad. The answer is yes. If the boiler pressure is too high, or in the red zone on your pressure gauge, there's an increased risk of leaks developing inside of the boiler.

Leaks can damage the boiler itself and also be harmful to those near the boiler as gas will be released which can have harmful effects on the safety, health, and well being of those in your household.

What Happens if Your Boiler Pressure Is Too Low?

It's not just high boiler pressure that can be an issue. If the boiler pressure is too low, the system won't work as well. An inefficient boiler isn't great for anyone.

So make sure your boiler pressure is neither too high or two low. It's a balancing act but one that is easy to achieve if your boiler system is healthy and well maintained.

Can a Boiler Explode from Low Pressure?

You may also be wondering if your boiler can explode due to low pressure levels, as indicated by the gauge on the boiler.

If the water level in the boiler is too low and the boiler has a corroded boilerplate or a faulty pressure relief valve, there could be an explosion. The boilerplate and pressure relief valve need to be maintained and can weaken over time.

Make sure to inspect them regularly to avoid a potentially catastrophic explosion in your home.

Can a Boiler Explode from High Pressure?

High boiler pressure, unlike low boiler pressure, will not cause your boiler to blow up. Still, high boiler pressure has other issues and should be dealt with as quickly as possible, as illustrated above.


If you have high boiler pressure that does not dissipate on its own, you will need to fix your boiler. You can make some changes yourself, but if you are unfamiliar with how the system works, you may want to hire a professional.

Like with most major systems, spending a little money upfront can save you hundreds if not thousands of dollars in the long run making it beneficial to do so.

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