Imagine coming back from work, you are tired, and wanting to take a shower, only to find that there is not any hot water. What a disappointment. Most probably the reason is low boiler pressure. With time a boiler can lose pressure due to obvious reasons like leaks and boiler faults. It affects it’s working and central heating. Fortunately, this issue is comparatively easy to diagnose and, in some cases, you can fix or repair it all by yourself.

In this article, we will have a look at the most common reasons for boilers losing pressure, how to fix it, and when it’s best to seek professional help.

Table of Contents

• What is boiler pressure?
• How to check if boiler pressure is low?
• Potential Reasons behind boiler losing pressure:
  • A leak in the pressure relief valve:
  • Bleeding of a radiator:
  • Leak in the heating pipework:
  • Problems with the expansion vessel:
  • Rusted or Broken boiler parts:
• How to fix a low-pressure boiler?
• Last Resort:

What is boiler pressure?

Mostly central heating components carry a volume of water, but unlike conventional style systems modern boiler does not use a water storage tank. They use an expansion vessel instead of the header tank. As we know, water volume increases and decreases with temperature, and the expansion vessel absorbs the pressure changes (rise and fall) of water when the boiler heats up the system water.

How to check if boiler pressure is low?

As a thumb rule, the normal boiler pressure should be between 1.0 and 1.5 bars. To check the boiler’s pressure for yourself, you just need to locate the pressure gauge on the front side of the appliance. The pressure gauge consists of two colors, red one and green one. Normally, when the pressure is low or below 1.0, you will find the gauge’s needle below the green section, and if the pressure is too high, the needle will be in the red section.

Potential Reasons behind boiler losing pressure:

If your boiler keeps losing pressure, then finding out the origin is the first step to fixing it. Some of the potential reasons behind any combi boiler losing its pressure are as follows:

• A leak in the pressure relief valve
• Bleeding of a radiator

• Problems with the expansion vessel
• Rusted or Broken boiler parts

Also Read: Top Ten Plumbing Fixes You Can Do Yourself

A leak in the pressure relief valve:

As the name shows, pressure relief valves are made to let out excessive pressure and that normally happens when the boiler exceeds 3 bars. When a valve becomes faulty no matter external or internal, it will start dripping water from the central heating system at a lower pressure to a pipe situated outside of the home. Check if the copper pipe is leaking, if that is the case, then call a professional to change the valve.

Bleeding of a radiator:

The Bleeding of a radiator is the reason behind the drop in the boiler’s pressure. This happens when you have recently had some work done to the central heating system. To fix bled radiator, re-pressurize the appliance. See, how to fix a low-pressure boiler? to re-pressurize your combi boiler.

Leak in the heating pipework:

To check if you have a leak in pipework, you will have to do some examining. Trace the pipes to locate the root cause of the leak. Mostly, leaking occur around the joint and bends as they are the weakest part of heating pipework. Temporary solution for a leaking pipe is to turn off the isolation valves for the heating circuit.

Problems with the expansion vessel:

Boiler pressure will rise to 3 bars when it heats up if you have a damaged expansion vessel. The reason behind this is the expansion of water in the system. Now the pressure relief valve lets out the excess pressure from the boiler, which results in an excessive drop in the pressure gauge. The repair of a faulty expansion vessel is neither nor hard to accomplish, however hire a licensed professional to take care of it.

Rusted or Broken boiler parts:

Rusted or broken boiler parts might be the reason your boiler is losing pressure. The boiler’s monitor shows when the appliance is not feeling well and need immediate attention. Replacing broken parts with new parts will solve the problem.

How to fix a low-pressure boiler?

The best way to top up the pressure on the boiler is by re-pressuring the system. You can re-pressurize it depending on the age and type of the boiler. See the manual first, if it states that it is safe to re-pressurize the boiler, then proceed. Re-pressuring of the boiler will usually comprise of the following steps:

1. Hit the main power supply switch, turn off the boiler and allow it to cool down.
2. Normally, combi boilers have an external filling loop to top up the boiler with water and increase the pressure.
3. Attach the filling loop hoses securely. Use a wrench to tighten the hoses if they are loose.
4. Open the filling valve located next to the filling hoses by using a screwdriver. Water will start flowing as soon as you open the valves.
5. Kill the filling valves when the pressure gauge reaches 1.5 bars.
6. Turn on the boiler’s switch. See if the boiler maintains the right pressure, if it does then the job is well done.

Last Resort:

If you tried everything given in this article and still have no luck in re-pressurizing your boiler, maybe it’s time for you to call a professional MEP (Mechanical, Electrical, and Plumbing) service in your area. Sometimes it’s best to have some professional help.