You should keep a regular check on your combi boiler to prevent issues later on. One thing to look at is the boiler pressure gauge. In the green zone or around 1.3 – 1.5 bar is good. Sometimes the pressure can get too high, and keep rising to 3 bar. Although not catastrophic, it can indicate a bigger problem about to happen.
Boiler pressure rising to 3 bar
High boiler pressure rising to 3 bar, although not dangerous in itself indicates another problem occurring in the system. Often, boiler pressure rises when too much water is added to the system when repressurising.
If the boiler pressure gets too high, the boiler has a built-in safety feature called the pressure release valve (PRV) which releases water to stop it from damaging the boiler.
When the pressure goes down, the boiler should fire up again as normal. The PRV is there as a failsafe in case the pressure within the combi boiler system exceeds 3 bar. In which case it will discharge before any damage is done to the internal workings of the boiler.
What is normal boiler pressure?
The ideal boiler pressure is between 1 to 1.5 bars when the heating is off. The pressure will rise anywhere up to 2.5 bars with the heating on and this is normal for most boilers. The manufacturer’s user manual will also state the ideal pressure and they usually mark the safe zone on the pressure gauge in green.
Checking if Combi Boiler Pressure Too High
First, locate the pressure gauge on the front of a combi boiler. It is a round dial usually found under the control panel. The dial shows the pressure reading in bars from 0 = no pressure, to 4 – very high pressure. The needle will point to the pressure reading both when the boiler is running and when it is idle.
Is high boiler pressure dangerous?
High boiler pressure can be dangerous as it can cause the boiler to overheat and potentially lead to a boiler explosion. It can also cause leaks and damage to the system. If you notice that the boiler pressure is consistently rising to 3 bar, then you should take immediate action to fix the issue.
You should check for any leaks in the system, release any excess pressure, and call a professional plumber to inspect and repair the boiler.
| Causes of Boiler Pressure Rising to 3 bar | Symptoms of High Boiler Pressure |
|---|---|
| Too much water in the system | Loud banging noises |
| Valves have failed | Leaks from the pressure relief valve |
| Expansion vessel problem | Fluctuations in the pressure gauge reading |
| Undersized expansion vessel | Unevenly heated radiators |
| Failing boiler parts | Boiler overflow pipe dripping outside the house |
| Blocked and damaged pipes |
Symptoms of high boiler pressure
If boiler pressure gets too high, it goes into the red zone and the boiler can develop faults due to the extra strain on the system. Certain parts within the boiler become prone to cracks and seals start breaking, resulting in water leaks. The boiler, if still running, becomes inefficient and has to work harder to get to the required temperature.
If the boiler overflow pipe is dripping outside the house, it can be a sign that the boiler pressure is too high. This can be due to a variety of reasons such as a faulty pressure relief valve, a faulty expansion vessel, or a blocked or damaged pipe.
Boiler overflow pipe dripping outside house
A sign of pressure build-up is the boiler overflow pipe outside the house dripping water. The overflow pipe is usually made of copper and goes through the outside wall. It can leak when the pressure release valve it is connected to in the boiler is either faulty due to sludge buildup or is not fitted correctly.
Causes of boiler pressure rising to 3 bar
1. Too much water in the system
When the pressure goes down in the central heating system for whatever reason, and you use the filling loop to re-pressurise it, the system can be overfilled, especially as you top up the water when the system is cold.
The filling valves may have been left open slightly by accident which lets water continue filling the system slowly.
2. Valves have failed
The valves used for filling could themselves fail, even if you have shut the handles tight. One of them could not be shutting down properly and the other letting water by which would go through the filling loop and pressurise the boiler.
3. Expansion vessel problem
Even after the pressure comes down on the boiler, if you find it goes back up again, this would indicate a problem with the expansion vessel inside the boiler. It may need servicing by being charged up or even replacing and a gas safe registered engineer will need to look into it.
The pipe that goes into the vessel can also become blocked leading to high boiler pressure and this should be checked too.
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4. Undersized expansion vessel
A large house with a big heating system usually requires a bigger expansion vessel. Normally, those within boilers don’t have a very large capacity and so may be undersized for the house.
You may need to install an additional EV outside of the boiler otherwise the high pressure problem can reoccur.
5. Failing boiler parts
Although the whole system is connected, the main boiler parts that closely relate to boiler pressure that could have become faulty and cause high pressure are the pressure release valve, expansion vessel, diverter valve and filling loop.
The engineer will check these closely when called out to this fault finding job.
6. Blocked and damaged pipes
Blocked and damaged pipes can cause the boiler pressure to rise to 3 bar. This can be due to a variety of reasons such as a buildup of debris or limescale, or a damaged pipe. To fix the issue, you should first turn off the boiler and allow it to cool down. Then, locate the blocked or damaged pipe and clear any debris or limescale buildup.
If the pipe is damaged, then it may need to be replaced. You should also check the pressure relief valve and expansion vessel to ensure that they are functioning properly.
What should boiler pressure be when heating is on?
The pressure gauge on a boiler will show anywhere between 1 and 2.5 bar when the heating is turned on. The upper limit will be shown on the green zone of the pressure gauge . It is important the boiler doesn’t stay over this limit. Each manufacturer sets its own upper limit but most go up to 2.5 bar.
Boiler pressure too high when heating is on
This can be caused by a number of factors, including a faulty pressure relief valve, a closed filling loop, or a faulty expansion vessel. When the pressure in a combi boiler rises too high, it can cause damage to the system and even lead to a dangerous situation. Therefore, it’s important to address the issue as soon as possible.
To fix high pressure in a combi boiler, there are several steps you can take. First, you should turn off the heating system and allow the boiler to cool down. Then, you can check the pressure gauge on the boiler to see if it’s above the recommended level of 1-2 bar.
What should boiler pressure be when heating is off?
When the heating is off, the boiler pressure should be around 1 to 1.5 bar. You can check the pressure gauge to confirm the pressure level. Boilers have a green zone marked on the pressure gauge where the needle should stay within at all times. Don’t let it go below this level. The user manual for the boiler will tell you exactly what they consider low pressure.
How to reduce boiler pressure
The following are the simple steps you can take to reduce your boiler pressure:
Use the magnetic filter on your boiler system
- Close the filling loop properly so no more water enters into the heating system
- Check the gauge to see if it’s showing pressure 2 bar or higher
- Turn off the boiler completely and let the system cool down
- Locate the valve at the bottom of the filter, and place a bucket under it
- Open the valve to let water out which will reduce the pressure on the gauge
- When pressure goes down to 1 bar, close the valve
The above method is the quickest way to get water out of the system. But not all boilers have a filter with them so the next method is also quick to do. You will probably need a spanner to open the valve:
How to use the drain off valve
- Close the filling loop properly so no more water enters into the heating system
- Check the gauge to see if it’s showing pressure 2 bar or higher
- Turn off the boiler completely and let the system cool down
- Locate the drain off valve which is usually fitted on the pipework near a radiator at the lower part of the heating system, usually downstairs in a hallway near a door.
- Put a container underneath the drain off valve ready to collect water
- Undo the valve (might need a spanner) on the drain off to release water
- When pressure reaches 1 bar, close the valve
The next method is mostly used to get rid of trapped air in the radiators but can also be used to drop the boiler pressure. It is a slower method overall though
Bleed a radiator to reduce boiler pressure
- Close the filling loop properly so no more water enters into the heating system
- Check the gauge to see if it’s showing pressure 2 bar or higher
- Turn off the boiler completely and let the system cool down
- Find the most convenient radiator to work with and place a container underneath the bleed valve
- Open the valve with a radiator key but resist the urge to open the valve too much as it can actually shoot out with all the water in the system, causing a mess
- When pressure goes down to 1 bar, close the valve
When the boiler pressure has come down and the heating is off
With the system cold, you should be aiming for 1bar pressure. The pressure may rise a bit as the system heats up and the water expands but it should only go up a small amount, to 1.3 or 1.4bar.
If it carries on rising to 2 or 3 bar, that indicates a problem with the expansion vessel, which may need servicing.
Boiler Pressure Too High Then Too Low
If the boiler pressure is fluctuating between too high and too low, it can be due to a variety of reasons such as a faulty pressure relief valve, a faulty expansion vessel, or a blocked or damaged pipe. It can also be caused by too much water in the system or a faulty pressure gauge.
To fix the issue, you should first check the pressure relief valve and ensure that it is functioning properly. You should also check the expansion vessel and make sure that it is properly charged with air. If the issue persists, then you should call a professional plumber to inspect and repair the boiler.
Summary
| What is boiler pressure? | Boiler pressure refers to the amount of pressure in a boiler system, which is usually measured in bars. |
| What is the recommended boiler pressure? | The recommended boiler pressure is typically between 1 and 1.5 bars when the heating is off. |
| What causes boiler pressure to rise? | Boiler pressure can rise due to a variety of reasons such as a faulty pressure relief valve, a faulty expansion vessel, blocked or damaged pipes, too much water in the system, or a faulty pressure gauge. |
| What are the symptoms of high boiler pressure? | Symptoms of high boiler pressure can include loud banging noises, leaks from the pressure relief valve, fluctuations in the pressure gauge reading, and unevenly heated radiators. |
| Is high boiler pressure dangerous? | Yes, high boiler pressure can be dangerous as it can cause the boiler to overheat and potentially lead to a boiler explosion. It can also cause leaks and damage to the system. |
| How can you fix high boiler pressure? | To fix high boiler pressure, you should first turn off the heating and allow the boiler to cool down. Then, you should check the pressure relief valve, expansion vessel, and pipes to ensure that they are functioning properly. You may need to release excess pressure by bleeding the radiators or call a professional plumber to inspect and repair the boiler. |
| Can bleeding radiators reduce boiler pressure? | Yes, bleeding radiators can help to reduce boiler pressure if there is excess air in the system. |
| What is a magnetic filter and how can it help with boiler pressure? | A magnetic filter is a device that captures debris and sludge in the boiler system, preventing blockages and damage. Using a magnetic filter can help to maintain the efficiency of the boiler system and prevent costly repairs. |
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