How to repressurise a Baxi boiler

How to Repressurise Baxi Boiler Pressure

Last updated on February 19th, 2024

Baxi boiler pressure should be between 1 – 1.5 bar on the pressure gauge when the heating is off and the radiators are cold.

I have been repairing boilers and central heating systems for over a decade and have come across every pressure problem.

Here I’ll give you my best advice for pressure problems on Baxi boilers based on my experiences.

Baxi Logo

Pressure Too Low

When your boiler pressure drops too low it will stop working, which means no heating or hot water.

Baxi boiler pressure too low
Low boiler pressure

To increase the boiler pressure, add more water to your heating system from the cold water supply via a filling loop.

Learning how to repressurise a boiler is very easy but very important.

The pressure rises when the heating is on, so you will not get the proper reading until it has cooled down.

If it is below 1 bar, you should top the pressure up. If you have to keep topping the pressure up, you have a problem that needs to be fixed.

Repressurise baxi boiler

How to Repressurise

If your boiler pressure drops below 1 bar you should increase the pressure.

How to increase the pressure on a Baxi boiler:

  1. Open one valve fully (only if there are two valves)
  2. Open the other valve slowly until you can hear the water
  3. When the pressure has reached 1 to 1.5 bar close both valves
  4. Reset the boiler (if needed)
  5. Turn the heating on

Do not open both filling loop valves fully straight away as the water pressure in the house might be too much for the boiler and cause the pressure to shoot up too much.

How to repressurise a Baxi boiler video

Filling Loops

A filling loop will be built in on the bottom of most modern and small combi boilers, but it could also be on the pipework.

Usually, this is below the boiler but there could be an external flexible filling loop anywhere on the system, sometimes hidden away in cupboards or behind boxing.

Filling loop open
External filling loop

There should be one of these types of boiler filling loops under your Baxi boiler:

  • Two Blue or Black Lever Handles: These will need turning a quarter turn each to open and close
Ideal Logic combi boiler filling loop
Baxi filling loop both blue valves closed

  • Easy-Fill Green Handle: This will simply need to be pulled and then released to stop filling.
Repressurising a Baxi boiler with filling link
Repressurising with filling link

  • Two Knobs: These will need turning anti-clockwise like taps to open, and fully clockwise to close.
Baxi boiler filling loop with two black knobs
Baxi filling loop with two black knobs

Pressure Keeps Dropping

If your boiler pressure is getting too low consistently, you will have a leak somewhere on your heating system, or the pressure relief valve is letting the water out.

To find out which it is, you can tie a carrier bag to the end of the copper blow-off pipe outside.

Boiler Leaking Water From Overflow Pipe
Boiler blow-off pipe

If it has lost pressure overnight, you should check the bag to see if it’s wet and if it is, that means the pressure relief valve is letting the water out.

An expansion vessel problem most likely causes this. If so, you will need to recharge the vessel or replace it if the diaphragm inside is split.

It could also mean the pressure relief valve is faulty and needs to be replaced.

Recharging expansion vessel on combi boiler
Recharging expansion vessel


If the bag is dry after your boiler loses pressure overnight you must have a leak on the central heating system which will need to be found and fixed.

A leak could be anywhere on the full system, boiler, radiators, or pipework under floors.

Lockshield radiator valve leaking
Leaking radiator valve

Pressure Too High

If you repressurise a boiler too much and cause the pressure to go too high, you will need to release some of the pressure.

Having the boiler pressure too high (above 1.5 when the system is cold), means you should let some pressure (water) out of the system to lower the pressure.

Baxi boiler pressure too high
Baxi boiler pressure too high

How to Release Pressure

To lower the pressure on a boiler you must let some water out of the central heating system.

There are a few ways to release the pressure.

bleeding water out of a radiator
Bleeding water out of a radiator

Here are my go-to ways to let water out of a heating system:

  • Bleed a Radiator: You can bleed water from a radiator bleed valve and catch the water in a bucket. This can take a while for the pressure to drop but a very common way to do it
  • Drain-Off Valve: Open a drain-off valve on the boiler or heating system with a hose attached and let the water out to drop the pressure
  • Pressure Relief Valve: Open the pressure relief valve on the boiler by turning the red plastic head
  • Crack a Nut: Crack a nut on the boiler heating pipes, or a radiator valve, with an adjustable spanner and catch the water in a tub
replacing radiator valve
Cracking a nut

Boiler Valve Positions

All the Baxi boiler valve positions below are fully open.

  • Black Valves: All 3 black handle valves in the photo are open as they are meant to be at all times. They are (from left to right) the heating flow, cold water inlet, and heating return valve.
  • Blue Valves: The blue handle valves are the filling loop valves which are fully open in the photo and are increasing the pressure. They should be closed unless repressurising the boiler.
Baxi boiler valve positions
Baxi boiler valve positions all open

Baxi Boiler Guides


If the boiler pressure gauge is reading zero (or close to zero) your boiler needs to be repressurised to get it working.

Repressurising a boiler is an easy job. It can save you from having to pay a plumber to do such an easy task.

If you have to keep repressurising your boiler you should get that problem found and fixed as soon as possible.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


What causes a boiler to lose pressure?

There are many causes for a boiler to lose pressure. The most common is a leak. Bleeding a radiator will always cause the pressure to drop.

Another cause could be the expansion vessel has lost its air and needs to be recharged or replaced. The pressure relief valve could also be letting water out. Or, the filling loop could be slightly open or damaged.

Do I need to turn my boiler off to repressurise?

No, you do need to turn your boiler off to repressurise.

It is recommended to do it when the heating is off and the system is cold as the pressure rises when the heating is on, but I repressurise boilers all the time when the heating is on.

How often should you need to repressurise a boiler?

A pressurised heating system is sealed so you shouldn’t need to repressurise it at all. If you get low boiler pressure often, you have a problem that needs to be fixed.

If you only do it once or twice a year, I wouldn’t worry about it as it’s such a small leak that it’s barely noticeable.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

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6 thoughts on “How to Repressurise Baxi Boiler Pressure”

  1. Hello Steven, the pressure on the boiler (Baxi Combi 105HE) has dropped to zero today (not sure if that was because I bled the radiators a couple of weeks ago). I have had a look at the pipe work but although there are black plastic valves (there’s a flexi loop) only the one on the right pipe and the one on the flexiloop turn and the other valve at the place where the flexiloop joins does not – I don’t want to force it. Only had the house a couple of months so not familiar with this boiler.
    Am I doing something wrong? Is it best to get a plumber out as I’m unsure?
    Thank you

  2. Hi

    Just need some urgent advice as heating company who maintains the boiler is closed on a Sunday. Baxi replaced an air pressure valve early last week as system was regularly losing pressure. System has since been constantly losing pressure (water on garage floor) – so we have been topping up daily with the easy-Fill green handle. This morning pressure at zero and the easy fill is not allowing water to flow to top up.

    Any quick fix ideas please?

    1. Steven Reid

      Hi Andy,
      No quick fix, you won’t be able to repressurise the boiler until the filling link is fixed or replaced.

  3. Hi Stephen I can’t find how to reduce pressure I made it go up too high would it be beside the tank ?

  4. J jones

    Boiler has blue and black knobs.
    One of the blue knobs is really solid and seems fixed.
    Boiler installed in 2018.
    Do I have to turn black knobs as well.?

    1. Steven Reid

      It should only be the two blue handles that need turned. They can be very stiff, you might need to use some pliers to turn it but once it’s turned it’ll be easy to turn again.

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