We've all been there - you go to run a nice hot bath after a long day, but the second you twist the taps... Gasp! Icy cold water starts to fill the tub.
Chances are, low boiler pressure is to blame for this.
The good news is that, in most cases, low boiler pressure is something you can diagnose and fix yourself without hassle.
So before you resign yourself to ice-cold showers and foot-warming sessions by the radiator, let's walk through the step-by-step instructions for increasing boiler pressure back to optimal levels.
In this guide, we cover:
What causes low boiler pressure?
How to check your boiler pressure
How to re-pressurise your boiler: A step-by-step guide
Signs you need to call a professional
What causes low boiler pressure?
Modern boilers are sealed systems, which means they should maintain the same water levels and pressure over time. However, there are a few common culprits that can gradually cause that pressure to drop:
- Leaks: Even small leaks from pipes, radiators, or the boiler itself will cause water to slowly escape the system, decreasing the overall pressure.
- Bleeding radiators: Bleeding your radiators to remove trapped air in the system can also slightly reduce the pressure. The air needs to be replaced with water to bring the pressure back within range.
- Faulty parts: Issues with certain internal components like pressure relief valves could also potentially cause pressure to drop (but these might mean you need a boiler repair).
A drop in boiler pressure is usually no major cause for concern. As long as you catch it and re-pressurise in time, your boiler should fire right back up.
If a bigger problem is at play, such as an internal leak or faulty component, never try to look inside your boiler yourself. Only professionals have the skills needed to do this safely, so always contact a Gas Safe registered JustFix engineer to help if you suspect something like this is causing your boiler’s pressure to drop.
How to check your boiler pressure
The water pressure gauge (often just a simple built-in metre) will tell you if your boiler's pressure is too low. This gauge is typically located on the front of the boiler, often near pipe connections.
For most boilers, the ideal operating pressure is between 1 and 2 bars. Anything under 1 bar will cause issues with your heat and hot water supply.
If the needle is teetering down towards 0, it's definitely time to re-pressurise!
How to re-pressurise your boiler
Bringing your boiler’s pressure back up to within the recommended range is actually pretty simple, so you shouldn’t need to contact a professional engineer in most cases.
How to re-pressurise a boiler with a filling loop
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Pro Tip: You’ll be able to tell if your boiler has an external filling loop because it’ll connected to your mains cold water supply and your heating system. |
Step 1: Turn your boiler off and allow it to cool completely.
If you aren’t sure how to turn your boiler off, refer to your manufacturer’s instructions.
Step 2: Identify the filling loop or valve on your boiler.
The filling loop is usually a flexible hose pipe with connections to the main heating pipes.
On most boiler models, it will be clearly labelled as the filling loop or have two valve taps sticking out. If you can't find it, refer to your manufacturer’s instruction manual.
Step 3: Turn both filling loop valves 90 degrees to fully open them.
This allows cold water from the mains to enter the system. When this is done correctly, you should be able to hear water flowing through the system.
Step 4: Keep both valves open until the pressure gauge reads between 1 and 1.5 bars.
The recommended pressure for your specific boiler model will be detailed in your manufacturer’s instructions.
Step 5: Close both filling loop valves tightly once you hit the right pressure level.
Step 6: Allow the system to re-pressurise completely by leaving it for 30 minutes to an hour before checking levels again.
If the boiler pressure drops repeatedly after you’ve re-pressurised it, this could be a sign that a bigger problem is at play.
Step 7: Turn your boiler back on and press the reset button if needed.
Boiler reset buttons are usually located on the main user interface panel for easy access. If you aren’t sure where yours is, refer to your manufacturer’s instructions.
Step 8: Stand back and admire the fruits of your handiwork.
You can also give yourself a pat on the back if you want to. Go on; you’ve earned it.
How to re-pressurise a boiler with an internal filling key
Don’t have an external filling loop? Don’t worry!
Here’s a step-by-step guide to re-pressurising your boiler using an internal filling key.
Step 1: Locate your boiler’s filling key (usually attached to the underside of the boiler’s tray).
Step 2: Insert the key into the keyhole next to your boiler’s manifold nut and turn to unlock.
Step 3: Turn the manifold nut clockwise with a wrench or spanner until the pressure gauge reads between 1 and 1.5 bars.
Step 4: Lock the manifold nut and key, and then remove the key.
How to re-pressurise a boiler with a hot water cylinder
If you have a system or standard boiler, you’ll have a separate hot water cylinder to store warm water and ensure there’s a constant supply throughout your home.
Increasing the pressure of these boilers can be a little different to a more straightforward combi boiler, but it’s still easy to do yourself.
Step 1: Locate the braided hose with a valve attached to the hot water cylinder.
Step 2: Open this valve while monitoring the boiler pressure gauge.
Step 3: Allow water to enter until the pressure reaches 1-1.5 bars.
Step 4: Close the valve once the recommended pressure is reached.
Signs you need to call a professional
While low boiler pressure is common and easy to fix occasionally, constantly having to re-pressurise could indicate a more serious underlying issue like:
- A major leak that needs locating and repairing
- A broken water valve or pressure relief valve requiring replacement
- Limescale buildup causing blockages
- General wear and tear if your boiler is quite old (i.e. over 10 years old)
If you find yourself having to top up the pressure more frequently, it's best to call a Gas Safe registered JustFix engineer to do a full diagnostic check.
They'll be able to pinpoint the root cause and make any necessary repairs to get your home’s central heating back to working properly.
Trying to repair a boiler yourself can be incredibly dangerous, so always leave it to the professionals who have the necessary skills and qualifications. If you don’t feel comfortable increasing your boiler’s pressure yourself, contact a Gas Safe registered engineer to come and give you a helping hand.
Book an expert heating engineer with JustFix
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FAQs about increasing boiler pressure
How often should you re-pressurise your boiler?
There’s no hard and fast rule for when or how often you should re-pressurise your boiler (sorry to disappoint you). Increasing boiler pressure is much more of an “as and when” task that some people will find they need to do more regularly than others.
Here are some rough guidelines for how frequently you should increase your boiler’s pressure:
- Whenever the pressure gauge drops below the recommended level (1-1.5 bars)
- After bleeding your radiators, as removing air from your central heating system will cause the internal pressure to drop
- If your boiler is older or not well-maintained (this can make minor leaks more likely)
Do you need any tools or equipment to increase a boiler’s pressure?
Beyond the filling loop, filling key, and a wrench to adjust manifolds, you don’t really need any special tools to increase your boiler’s pressure.
You might find it helpful to have a torch (especially if your boiler is in a cupboard) and an old towel to catch any water drips when you disconnect the filling loop hose.
How do you know if your boiler has a filling loop or filling key?
If you have a filling loop, there will be a flexible silver hose or pipe with valves on each end. The loop might be detachable and stored near your boiler when it’s not being used.
If you have a filling key, look out for a small keyhole next to the manifold or valve on your boiler. This is where the key is inserted. Usually, filling keys are attached under the boiler tray.
If you still aren’t sure what type of filling tool your boiler has, check the manufacturer’s instructions for your specific model or contact a professional heating engineer.
