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How to Repressurise a Boiler

How to repressurire a boiler

Every household should have a water heating system, like a boiler. If you’re lucky, you spend your days without sparing a single thought on how it operates.

However, if you’re reading this article, chances are you need help with your boiler.

Maybe you’ve noticed some warning signs, or your central heating system has stopped working. If there’s no heat and no hot water, it’s a sign that there’s something wrong with your boiler.

Fortunately, you can try and fix this issue on your own. Most likely, repressurising your boiler is the best solution.

Read on to find out how to do that!

How to Check Boiler Pressure

Checking boiler pressure is very easy.

First, you have to identify the pressure gauge, which looks like a round dial. Modern systems, such as combi boilers, feature a pressure gauge on the front or under the control panel.

Then you can analyse what you see. Normal boiler pressure should be between 1-2 bars.

The gauge often indicates this optimal range by marking it green. 

Red zones at both ends of the gauge indicate too low or too high boiler pressure.

However, some heating systems feature a digital gauge. In these cases, when the pressure in the system is too low or too high, you’ll see a flashing pressure reading with a pressure warning.

When Boiler Pressure Is Too Low

If you think your boiler needs repressurising because the pressure is too low, look for these symptoms:

  • The radiators aren’t warming up properly
  • Central heating is not working
  • There’s no hot water
  • The dial on the boiler pressure gauge is low

There are two main causes as to why your boiler pressure could be too low:

  1. Bleeding radiators.

    When you’re bleeding the radiators, you remove air from the boiler system, which changes and lowers boiler pressure.

  2. Leaks.

    To check whether your boiler is leaking, look for damp patches near the boiler, pipework, and radiators, water stains on a ceiling below the boiler, rust marks, bubbling or flaking of paint, and swelling, bulging or lifting of the skirting board.

    Also, remember not to open the boiler and look for leaks inside.

Additionally, low water pressure may be caused by a boiler fault. In many cases, the problem lies in the boiler filling loop system, featured in modern combi-boilers.

As such, if you can’t figure out the reason why your boiler is losing pressure, get in touch with an expert.

How to Increase Boiler Pressure With a Keyless Filling Link

If your boiler pressure is too low, you can increase it by following this step by step guide:

  1. Turn off the boiler and wait for it to cool down.

  2. Find an external filling loop (or a filling link).

    It’s a short, braided hose linking two water pipes, with levers at both ends, that should be located directly under the boiler.

  3. If you still can’t find it, consult the manual – your boiler might have a keyed filling loop or keyless internal filling loop.

  4. Align the levers with the direction of the external filling loop by turning both valves.

    The boiler pressure gauge should be going up, and you should hear water running.

  5. Shut off both valves when the pressure reaches 1.5 bar.

  6. Turn on the boiler if there are no leaks and the water pressure stays up.

  7. Check the pressure once again after the boiler has cooled down and has been in operation for some time.

  8. Be careful not to accidentally over-repressurise your boiler.

    When it happens, you’ll have to reduce boiler pressure.


How to Repressurise Your Boiler with a Filling Key

You can also repressurise your boiler with a filling key – it depends on the type and age of your water heating system. To do it, follow these steps:

  1. Switch off your boiler and let it cool down.

  2. Pull out the tray underneath your boiler and remove the key.

  3. Look for the key manifold keyhole, it should be located next to the square manifold nut.

  4. Insert your filling key into the key manifold and turn it approximately 45 degrees to the unlocked position. 

  5. Observe the arm on your boiler’s pressure gauge.

    As the pressure begins to rise, it will move up.

    When the gauge reaches 1.5 bar, turn the manifold nut clockwise and double-check the gauge settles at this pressure.  

  6. If the gauge fails to stay in the green zone, turn the release knob on a nearby radiator to lower the pressure on your boiler. 

  7. Turn the manifold nut and the manifold key back to the locked position.

  8. Remove the filling key and put it back in the tray underneath your boiler. 

  9. Switch your boiler back on and observe.

Is It Dangerous?

Rest assured, a boiler with a pressure that’s too low or too high doesn’t cause any safety hazards.

Your heating system should have a pressure relief valve (PRV) that lets water escape and prevents damage. Some systems also shut down automatically in case of excessively high water pressure.

What’s more, you can repressurise a boiler on your own, which is a straightforward procedure.

However, don’t hesitate to call a professional if you have to repressurise your boiler over and over again, and the pressure keeps dropping.

You should also contact a heating engineer in the case of excessive leaks. A boiler can still be in operation when left unchecked.

Still, it may break down in the worst possible moment, and you can easily prevent that by contacting an expert.

The Bottom Line

As you can see, there’s nothing difficult in repressurising a boiler.

Even though you may have no idea about boiler maintenance, you can fix any issues in the case of low and high pressure, and adjust it accordingly. Checking the pressure on your boiler is also easy, and you should inspect your boiler and its surrounding areas for any concerning signs.

Ultimately, call a professional if you think you can’t deal with a certain problem on your own. An expert will recognise the issue and fix it in no time. As a result, you won’t have to worry about your heating system shutting down unexpectedly.

Need help with your boiler?

Contact B.Wilson Plumbing and Heating – our highly qualified engineers are on the ready to support you and fix your plumbing and heating in no time.

With our 5 star service and high standard of workmanship, we’ll make sure you’re looked after every step of the way.



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