Low boiler pressure can wreak all kinds of havoc on your heating system - it could leave you with no hot water and no heating. Luckily, it’s a relatively easy fix that you can do yourself at home. Read on to find out more about what to do if your boiler pressure is too low, including how to fix it.

1. What is boiler pressure?

To understand low boiler pressure, it’s important to first understand what boiler pressure is. Boiler pressure is essentially the amount of water in the heating system at any time. Too much water and the pressure will show as too high, but too little water and it will show as low. Boilers have a pressure gauge located on the front that will tell you the current pressure of the system.

2. Why is the boiler pressure too low?

There are two main causes of low boiler pressure:

  • Leaks in the system
  • You’ve recently bled your radiators

When you have a leak, even if it’s a slow leak, the amount of water in the heating system is being reduced, and therefore causes the pressure to drop. It’s important to find the source of the leak so you can get it under control, and then you can use the filling loop to add more water to the system. Start by checking the pipes around your boiler and radiators for signs of moisture. You should also check your ceilings and floors for damp patches.

If you have recently bled your radiators, the pressure will drop slightly because you’ve released the trapped air in the system. This air needs to be replaced with water to get the pressure back up again. 

3. How can I check my boiler pressure?

You can check your boiler pressure using the pressure gauge located on the front of your boiler. You’ll see that it goes from 0 to 4 bar of pressure. A boiler that is off should sit at around 1 bar of pressure. A boiler that is heating your house should be around 1 to 2 bar.  

If your pressure gauge looks like this, either when the radiators are cold or warm, then the pressure is good.

If your boiler’s pressure gauge looks like this, then the pressure is too low and needs to be increased.

4. How to fix low boiler pressure

If the boiler’s pressure gauge is showing low pressure, as above, you can fix the issue by adding more water to the system. Before you do this, it would be a good idea to check for leaks to ensure that isn’t the reason for the low pressure.

If you have done this, you can follow the steps below to increase the pressure of your boiler. If you’re unsure of anything or can’t find the filling loop, contact the manufacturer or check their website for guides on your specific model of boiler.

  1. Turn the boiler off and wait at least an hour for the water to cool down.
  2. Attach the filling loop at both ends (one end to the boiler and one to the mains water valve)*.
  3. Open both valves of the loop to allow fresh water to enter the system.
  4. Keep an eye on the pressure gauge and continue to let water in until it reaches 1.5 bar.
  5. Close both valves, one first and then the other.
  6. Turn the boiler back on. Some may require you to reset them by pressing the ‘reset’ button.
  7. Undo the filling loop from both ends, using a towel to catch any excess water that may drip out
  8. Keep the filling loop in a safe place until you need it again.

*If your boiler has an internal filling loop, you don’t need to attach it yourself. Instead, you can flick the switch on the valve to open it. 

5. When should I call a Gas-Safe engineer?

You should call a Gas-Safe engineer to check over your boiler if you’ve repressurised the system but the pressure has dropped again or if you are continually increasing the pressure. It could be a sign that there’s a leak elsewhere that you haven’t noticed or it could be an issue with your boiler. The engineer may be able to provide some advice or fix the problem for you.

Should you notice a leak in your system, don’t try to increase the low pressure yourself. Instead, call a reputable heating engineer to look at your heating system for you.


  • Check the pressure gauge on the front of the boiler to see if it has low pressure.
  • Causes of low pressure include leaks and recently bled radiators.
  • The boiler’s pressure should sit between 1 and 2 bar
  • You can increase the pressure by putting more water into the system via a filling loop.
  • Call a Gas-Safe engineer if the problem isn’t resolved.

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