How do I repressurise my boiler?
Have you noticed your radiators aren’t heating up properly? Or maybe your hot water taps have become unreliable? This often points to one simple issue: your boiler pressure is too low. When that happens, you’ll usually need to repressurise your boiler.
Although it sounds technical, most homeowners can manage it themselves. In this guide, we’ll walk you through how to spot low pressure, why it happens, how to top it up and when to call an engineer.
Key takeaways at a glance:
- Low boiler pressure is usually easy to fix at home by topping up the system to the ideal 1–1.5 bar
- If your boiler keeps losing pressure, common causes include small leaks, bleeding radiators or cold weather
- Repeated drops mean it’s time to call an engineer
Watch: How to bleed and repressurise a boiler
How to know if my boiler pressure is low
Low pressure often shows up through issues such as:
- Showers not getting as hot as usual
- Radiators feeling colder than normal
- The boiler shutting down intermittently
To confirm, check the pressure gauge on the front of your boiler. Most boilers operate best between 1 and 1.5 bar when cold. If it’s under 1 bar, it’s time to top up.
Your boiler manual will confirm the ideal range for your model.
Why does my boiler keep losing pressure?
The most common causes are:
- Small leaks in radiators, pipework or valves around the boiler
- Bleeding radiators, which can release some system water
- Cold weather, which can cause slight drops
If your pressure keeps falling, even after topping it up, there may be an underlying fault that needs investigation.
Is it safe to repressurise a boiler yourself?
Yes. Repressurising a boiler is usually safe and straightforward. It won’t cause damage as long as you follow your boiler instructions.
However, if you have any problems, the pressure repeatedly drops after resetting or you notice damp patches or leaks, it’s best to call an engineer
How do I increase the pressure on my boiler manually?
Before you begin, check whether your boiler uses an external filling loop or an internal filling loop/key.
Repressurising using an external filling loop
- Turn off the boiler and let it cool completely
- Place an old towel underneath to catch any water spills
- Locate the external filling loop – a flexible braided hose with valves at each end – and make sure both ends are securely connected
- Open both valves slowly to allow cold mains water into the system
- Watch the gauge rise. Once it reaches 1–1.5 bar, close both valves
- Remove the filling loop if your boiler requires it to be disconnected
- Switch the boiler back on and check the pressure again
How to repressurise a Worcester Bosch boiler
Worcester Bosch boilers use an internal filling key.
- Place a towel underneath the boiler
- Remove the underside hatch and take out the internal filling key
- Locate the filling link – a small slot next to a white square knob
- Insert the key until the arrow almost lines up with the black plastic
- Turn the key anti-clockwise so the arrow faces you
- Turn the white square clockwise to allow water into the system
- Once the gauge reaches 1–1.5 bar, turn the square back to its starting position to stop the water
- Remove and dry the key, then replace the hatch
- Switch the boiler back on and check the pressure
How often should I check the pressure on my boiler?
Check your boiler pressure at least once a month.
If you bleed radiators, check again immediately afterwards – this is one of the most common reasons pressure drops!
What to do if the pressure doesn’t increase or drops again quickly
If your boiler won’t repressurise, or the pressure falls again soon after topping up, it’s best to contact a heating engineer.
A persistent drop usually means:
- A hidden leak
- A faulty pressure relief valve
- A damaged expansion vessel
Some leaks may be visible, but others can be tucked away in hard-to-reach or unsafe areas. An engineer will safely diagnose the issue and prevent further damage.
Custom Heat can support you
There’s never a convenient time to lose your heating or hot water. With Custom Heat, you can book a callout in just two minutes using our simple online booking system.
If your boiler keeps losing pressure, we’ll diagnose the cause and get your heating working again quickly.
| For year-round reassurance, our Boiler Cover & Care Plans include same-day callouts and an Annual Boiler Service from just £12.50 per month. Get a boiler care plan quote |
FAQs – How do I repressurise my boiler?
What does repressurising a boiler mean?
Repressurising means topping up the water pressure in your heating system so your boiler can run efficiently. This is usually done using an internal or external filling loop, or a filling key on Worcester Bosch models.
Why does my boiler keep losing pressure?
Common causes include small leaks, radiator bleeding, faulty valves or expansion vessels. Pressure also drops during cold weather. If the pressure falls repeatedly, have an engineer inspect the system.
Is low boiler pressure dangerous?
No. Low pressure isn’t dangerous, but it can prevent your boiler from working and may indicate a leak. Persistent low pressure should always be checked by a professional.
Who can fix a boiler with persistent pressure loss?
Only a Gas Safe registered engineer is legally qualified to work on your boiler. Custom Heat can quickly diagnose pressure issues, repair faults and get your system running smoothly again.
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