Boiler is Losing pressure. What To Do?

As the leading Boiler Installation Company covering Nottingham, we are used to seeing a variety of issues with boilers. A substantial number of problems that your boiler faces are usually rooted in boiler pressure. Boiler pressure is such an essential part of boiler functions. If it goes too low, the boiler will cut out to prevent damage.

Even though the problem sounds dire, the good news is low boiler pressure is easy to diagnose and, in most cases, it’s also easy to fix without the assistance of a Gas Safe engineer. In this guide, you get to learn about the most common boiler pressure problems and the possible fixes that you can try out before calling out an expert.

What is Boiler Pressure?

A boiler heats cold water that flows around a circuit of pipes and radiators around the house. For the process to be efficient, the pressure needs to be stable. In most modern boilers, there’s a filling loop which is used to maintain the pressure.

The loop connects to the cold water pipe and when the pressure drops, you can use it to increase pressure and restore the normal functioning of the boiler.

What causes boiler pressure to drop?

There are various culprits in low boiler pressure. But, there are two that stand out:


If your central heating has a leak, the water lost through the leak causes the boiler pressure to drop. Unfortunately, leaks can go unnoticed for some time and the gradual drop in pressure masks them very well.

If you notice you have to top up the boiler pressure more often, it could be caused by a leak. Try looking for damp patches around pipes, radiators, and the boiler. But, don’t look for the leaks inside the boiler. That’s a job best left for the professionals.

If you find the leak, you should call a Gas Safe registered engineer who will fix the problem. In some cases, leaks are not only the result of a worn-out pipe. They can also be caused by failing valves or worn out seals.

Bleeding radiators

If you’ve heard to bleed your radiators recently, you might have lost some pressure. When you bleed the radiators, the air is released. It lowers the pressure inside the boiler system which might cause a broad range of problems.

Read our latest blog: Boiler Doesn’t Respond to Thermostat…What to do.

How can I check the pressure on my boiler?

If this strange problem is happening to you for the first time and you’re not sure where to start, it’s best to start by checking if the pressure of your boiler is right.

The process of checking the pressure will depend on the type of pressure gauge you have. If it’s a hydraulic gauge, you will see the low and high-pressure levels by red sections on the dial.

If you have a digital gauge, you see a flashing pressure reading. You will also be notified if the pressure reading is too high or too low.

Pressure readings below 1 bar are considered dangerously low. If the pressure falls below 0.5bar, most boilers won’t work.

The ideal pressure setting for your boiler is between 1.5 to 2 bars. If the pressure goes above 2.75 bar, you need to bleed the radiators down to 1.5bar.

Can I Fix low boiler pressure myself?

Most low boiler pressure systems are easy to manage and you can easily fix them without the help of an expert. However, this is only advisable if you know your way around the boiler. If it’s your first time, call in an expert who can walk you through the steps before attempting it yourself.

How to re-pressurise the boiler

The first step to repressurising the boiler is to check the user manual and make sure it’s safe to proceed.

You need to find the filling loop on your boiler. It differs depending on the age and design of the boiler. Some have an actual filling loop while other boilers use a filling key and a manifold nut. Once you locate the appropriate filling system, you can follow the steps below carefully.

  • Switch off the boiler and allow it cool down completely
  • Check the ends of the filling loop and make sure they are securely attached
  • Open both valves to allow water from the cold mains into the boiler. You can hear the water flowing into the system
  • As the water flows into the system, check the pressure gauge so you don’t overfill the system. It should go up to 1.5 bar.
  • After you attain the optimum pressure for the boiler, you can close both valves one after the other.
  • Double-check to make sure you have the right pressure then proceed to switch the boiler back on.
  • In some cases, you might need to press the reset button to clear the error
  • After the boiler fires up correctly, undo both ends of the filling loop. Take precaution to catch any water spillage and keep the filling loop safely. You will need it again.

Even though it sounds serious, you can easily re-pressurise your boiler at home. However, if you’re unsure of anything, it’s best to have an expert deal with the problem while you learn so you can do it yourself the next time.

If you notice a leak, have it fixed as soon as possible. That will protect the boiler from further damage and also curb the cost of having the leak fixed.

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