Low boiler pressure and how to fix low pressure in your boiler

Low boiler pressure is the most common boiler fault that can cause a gas boiler not to work. If your boiler stops working and you check your pressure gauge, low pressure would be a good outcome. 

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This is due to the fact that it can easily be fixed and your boiler will start working again in no time. Simply repressurise your boiler and it will either start up again or if not, hit the reset button and that should be that.

If you want to know why your gas boiler is losing pressure then here are a few reasons and what to do next. 

Low boiler pressure – what is it and how to fix it?

Low boiler pressure is where too much water has escaped out of your central heating system. This can happen in a few ways, but usually, it is because of a leak or gap in the pipework. Your boiler needs to have a certain amount of water pressure to be able to work properly. 

Boiler pressure should usually be between 1.5 bar and 2 bar.

Old boilers losing pressure

Old boilers are more likely to naturally lose pressure. This is because there will be tiny gaps in parts that will gradually let tiny steam droplets out as they are working. This is however inefficient so it may be a good idea to consider how much a new boiler costs and see if it is worth it in the long run.

New boilers losing pressure

New boilers losing pressure is far less common but it does happen, but if this is the case you may want to contact the installer or the manufacturer depending on how long ago your boiler installation was. Most new boilers such as the Worcester Bosch 4000 or the Viessmann Vitodens 050-w can also tell you on their LCD screens what the issue is too very easily.

Most common reasons for low water pressure in a boiler

The most common reason to check your boiler water pressure is that your heating isn’t working. So, if you have checked the pressure gauge and it is below 1 bar (pressure measurement) then your boiler will likely be switched off to save it from doing any more damage to itself. Here are the usual reasons why water pressure in your gas boiler is low:

A leak in the boiler or central heating system can cause pressure to drop

More often than not a boiler leak in your central heating system will be the cause of your low-pressure problems. This could be a broken seal, pressure valve, or heat exchanger. Whilst the pressure can be made higher unless sorted the pressure will drop again and again.

Frozen pipes can cause low water pressure in a boiler

Frozen pipes can cause blockages stopping water from circulating properly, and therefore water not reaching the whole way around the central heating system. This will then register as lower pressure on the gauge until it is thawed out. 

Radiators need bleeding or air is trapped in the system

Overtime air can get into your central heating system and as this builds up it can cause pockets of air in your radiators and pipework. If this is the case then you will be able to tell that your radiators are hot in some places and cold in others. Ideally, you need to bleed all the air out which will lower the pressure even more initially but once topped up, it will be back to normal.

How to fix low pressure in a boiler

If your boiler has flagged up a fault such as E1 error code then you need to check the pressure.

To fix low water pressure in a boiler you need to open up the filling loop. This is 2 taps next to each other that when opened will let cold water into the system, filling it back up again. Here’s how to do this including where to find your filling loop.

  1. Safety first, switch off your boiler and let it cool down. This will ensure that the water in the system is as little pressurised as possible so you can get as much cold water in as needed.
  2. Find your filling loop. This is usually at the bottom of most boilers just underneath. There will be 2 taps close to each other on the same pipe, or loop as it is known.
  3. Open one of the taps, and then the other so that they are both open at the same time. You should hear water flowing like you would when a hosepipe is turned on. 
  4. Once open you need to be checking the pressure gauge on your boiler constantly and wait until the needle on the dial reaches 1.5 bar. Some boilers have a green area to make it easier to spot.
  5. Once the pressure gauge is at the right level of 1.5 bar, then you need to close one of the taps to stop the flow of water, and then close the other one to ensure that no more water will get in or out. 
  6. You can then switch on or reset your boiler and it will be a good idea to keep checking your boiler pressure over the next few days. 

Should I call a heating engineer for low boiler pressure?

Now right away no. If you can manage to top up your boiler pressure and it stays at the right level on the pressure gauge then you will be fine. If your gas boiler pressure is dropping as often as monthly then you would need to get it checked.

A Gas Safe registered heating engineer will be able to check over your boiler and pipework to see where the pressure is dropping and give you an idea of whether it is a new pipe seal or in the worst-case scenario, a new boiler. 

Why is correct boiler water pressure important?

If your boiler water pressure is set at the right level, then this is when your boiler works at its most energy-efficient. An energy-efficient boiler uses less gas and electricity, therefore, saving you money on your utility bills. It also means that the boiler is in good working order and should be checked every year with a boiler service. 

Do I need a new boiler if the water pressure is too low?

No. low water pressure is a common boiler problem that can usually be easily fixed. High water pressure on the other hand can tend to mean more problems or in worst-case scenarios, boiler explosions.

If there is too much pressure, and bleeding radiators didn’t work, then there is usually something causing the issue that needs fixing. If you are curious, get online boiler quotes now just in case.

What is the right boiler water pressure?

The correct water pressure in a boiler is between 1 bar and 2 bar. 1.5 is the best option to aim for as water pressure can fluctuate when water is heating up and cooling down. This protects your boiler from breaking down. 

I can’t find my filling loop to top up the pressure?

If you can’t find your filling loop at the bottom of your boiler then you may have a newer boiler that has an internal filling loop that can be controlled with buttons or in some cases, can be automatic like the Worcester Bosch 8000. If you can’t find your cold water pipe filling loop then you may need to consult that manual for your boiler model. 

Is low water pressure dangerous?

Low water pressure isn’t directly dangerous as most boilers will just not work or switch off. The issue with it is that it may be caused by a leak which could be dangerous and cause more problems. If you are trying to top up your boiler water and the gauge isn’t moving, do not just leave it on, it should move straight away. 

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