Home Improvement

Why Does My Boiler Keep Losing Pressure? – Reasons and Solutions

Image source: Yevhen Prozhyrko / Shutterstock.com

Some household appliances are a bit more capricious than others and your boiler is definitely one of them. Raise your hand if you have been a victim of low water pressure and had to take that long and disappointing shower after work. Yup, it’s not the most pleasant experience. But before you start looking for a new boiler, hear us out:

There are easy ways to find out exactly why your boiler’s pressure keeps dropping and even easier solutions to resolve the issues. And, in this article, we are going to cover all of them.

Table of Contents:

What is boiler pressure?

We know that the term may sound a bit hard to understand, intimidating even, but we’ll explain it as simply as possible. Basically, boiler pressure is the balance between water and air inside the appliance.

When the pressure is too low, it means that there isn’t enough water in the sealed system of the boiler and you’ll start to experience a weird flow. This applies to both regular and combi boilers.

Reasons for low boiler pressure

There could be several reasons for your boiler’s pressure drop. Let’s take a look at the possible culprits:

There are leaks in the pipework

This type of plumbing problem is one of the hardest to spot. You can probably figure out why by yourself. Most of the pipework in your property is concealed by walls or hidden behind cupboards. And having a leak behind one of your walls doesn’t end only with low boiler pressure. Your home will also suffer consequences like the appearance of nasty mould and even damage from rot.

Still, with all of that being said, most leakage problems regarding your heating system will occur at visible spots like joints and fixtures. It’s quite possible that your boiler is leaking water from the bottom. Check the supply pipes to your radiators as well. Is the paint flaky or bubbling? If yes, then congratulations – you’ve found a potential leak. Other indicators include rust, swelling or lifting of the skirting board and water spots.

Recently bled radiators

Another probable cause for the low pressure on your boiler is a recently bled radiator. So, if you’ve tried to make your home heating system work better and right after that you noticed the water flow acting strangely, you’ve got your answer.

Your radiators are full of air

Have you had any work done to your heating system and noticed that your boiler keeps losing pressure? There is a big chance that your radiators and towel rails have trapped more air than needed.

To fix the problem, try releasing the extra pressure with the help of a bleed key. To do this, just slightly open the vent with the above-mentioned tool. The radiator will start making a very specific hissing sound and, after that, it will let a little water escape. Once this happens, you can close the vent again. Repeat the process for every radiator in your property. Like we said earlier, too much bleeding can lead to low boiler pressure, as well, so be careful.

A faulty boiler

So, you’ve checked your whole house for leaks and other non-boiler related elements but the pressure keeps dropping on your boiler. What now? Well, at this point the source of your problem is most likely the actual heating appliance.

If you own a combi boiler, you can try fixing the issue by manually adjusting its so-called “filling-loop”. This part of the appliance maintains the cold water pressure from the mains supply. Of course, before you proceed with the task of repressuring the boiler yourself, you need to check the instructions for more details. If you don’t find any in your manual, we don’t advise continuing with the task. In such situations, it’s better to get a certified expert to solve your problem.

A damaged pressure gauge

The chances of this happening are quite low but they are still there. Check if the pressure gauge is reading correctly. If you try to top the pressure and the gauge doesn’t register the change, you must take immediate actions, because having such an issue with your boiler is very dangerous.

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The pressure relief valve is damaged

The normal stats of a boiler are between 1.0 and 1.5 bars. Some models can reach up to 3. When this happens, this part of the appliance releases the “extra” pressure. If the valve is damaged in some way, the boiler will start to show signs of lower pressure. The bad news is that you can’t fix this part of the appliance yourself and you’ll have to call in a professional.

There are many things that can go wrong inside your appliance. Some of them you can fix yourself, while others will require the attention of an expert. Well, now you know the most probable causes for low boiler pressure.

How to repressurise a boiler correctly

To adjust the boiler pressure, you can check your manual and if it says that you can repressurise the boiler yourself, proceed with the following steps:

  1. Locate the filling loop and pressure gauge.

    Find the filling loop on your boiler and the pressure gauge, as well. The handles of the filling-loop must be set at a 90° angle to the flow of the pipe.

  2. Shut off the boiler.

    Turn off the heating appliance.

  3. Turn the filling loop handles.

    Set the two filling-loop handles in the direction of the pipe. After you do this, you’ll start to hear the sound of flowing water.

  4. Adjust the filling loop.

    Keep a close eye on the pressure gauge while you’re adjusting the filling loop. You are looking for a pressure level at around 1.0 – 1.5 bars. This rule applies to most boiler models. If you are not sure about yours, check the manual again.

  5. Keep watching the pressure gauge.

    Don’t stop watching the gauge – you have to be very careful not to over-pressurise the appliance. If the gauge is located on a weird part on your boiler, you’ll need to get somebody to help you out.

  6. Close the filling loop handles.

    Once the correct pressure is reached, make sure the handles are fully closed and turn the heating appliance on.

If you happen to overpressurise your boiler, just bleed your radiators by following the steps we described earlier in the article.

Get help from a professional

If you try everything we’ve mentioned in our article and your boiler pressure keeps dropping to 0, it’s time to call a professional to resolve the situation. Fantastic Services offers expert boiler repair services, performed by experienced electricians and gas safe registered engineers. We can repair any type or brand of boiler and also provide you with a 1-year guarantee on labour and all parts.

Don’t waste time on troublesome tasks and leave everything to Fantastic Services today! To make things even more, easier for you, we offer boiler cover plans to help you keep your heating system in its best condition.


  • Faulty pipework is a huge problem and not just regarding your water pressure. If you happen to spot a leak somewhere in your house, take immediate actions to fix it, otherwise, you risk causing even more damage to your property.
  • Make sure to check the instructions manual before you proceed with any type of work on your boiler. If you don’t find specific information on how to repressurise it, it’s better to call a pro to fix it for you. 
  • If you decide to repressurise the boiler yourself, make sure to keep an eye on the gauge, so you don’t overpressure the appliance. You don’t want to go back and forth between bleeding radiators and re-pressuring your boiler the whole day. 


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