Baxi Boiler Pressure Help Guide: Too Low & Too High Fixes

Last updated on October 5th, 2023

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

Anything below this is too low and anything above is too high and can cause your Baxi boiler to not work.

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

Here I’ll give you my best advice for Baxi boiler pressure problems based on my experiences over the years.

Correct Baxi Boiler Pressure

A Baxi boiler will work when the pointer on the gauge is in the green zone but anything in the red zone can cause your boiler to stop working.

The big green triangle on the pressure gauge is where you ideally want it to be when the system is cold. Heat will cause it to rise, which is perfectly normal as long as it doesn’t go to the red zone.

Baxi Boiler Pressure Too Low

When your Baxi boiler pressure drops too low the boiler will stop working which means you will have no heating or hot water.

To increase the pressure, you must 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

If your Baxi 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 Baxi boiler pressure to shoot up too much.

Filling Loops

A filling loop will be built in on the bottom of your boiler on 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.

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

• Two black or blue lever-type handles: These will need turning a quarter turn each to open and close.

• Easy-Fill green handle: This will simply need to be pulled and then released to stop filling.

• Two knobs: These will need turning anti-clockwise like taps to open, and fully clockwise to close.

Baxi Boiler Keeps Losing Pressure

If your Baxi 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.

If your Baxi boiler has lost pressure overnight again, 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.

This is most likely caused by an expansion vessel problem. 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.

Leak

If the bag is dry after your Baxi 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.

How Often Should You Need to Repressurise a Baxi Boiler?

A combi boiler is a sealed pressurised system so you shouldn’t need to repressurise it at all.

If you need to repressurise your Baxi boiler often, you have a problem that you need to fix.

If you need to repressurise your Baxi boiler once or twice a year, I wouldn’t worry about it as it’s such a small leak that it’s barely noticeable.

Undersized Expansion Vessel

Baxi boilers are sometimes undersized when fitted and the expansion vessel in the boiler is not large enough to cope with a large house’s central heating system.

This can cause problems with the pressure.

Getting the best combi boiler for a large house is very important, but adding an external expansion vessel, that is large enough for the central heating system, is also an option rather than upgrading to a bigger boiler.

Baxi Boiler 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 Baxi 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.

How to Release Pressure on a Baxi Boiler

Knowing how to release pressure on a Baxi boiler might save you from some boiler problems.

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

There are a few ways to release the pressure on a Baxi boiler.

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

• Bleed a Radiator: You can bleed a radiator from a bleed valve and let the water squirt out into 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 central 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 Baxi boiler by turning the red plastic head
• Crack a Nut: You crack a nut on the boiler heating pipes or a radiator valve with an adjustable spanner and catch the water in a tub or bucket

Baxi 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 Baxi boiler pressure. They should be closed unless repressurising the boiler.

Baxi Boiler Guides

• Baxi boiler no hot water
• Replace pressure relief valve on Baxi boiler
• Baxi E119 fault code repair
• Baxi E133 fault code repair

Summary

It’s good to know for sure what the problem is when your Baxi boiler is not firing up but the first thing you need to check is the pressure gauge.

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

Repressurising a Baxi 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 Baxi boiler you should get that problem found and fixed as soon as possible.

Feel free to leave feedback or 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.

---

Baxi Boiler Pressure FAQs

---

Can you repressurise a Baxi boiler by yourself?

Yes. You can repressurise a boiler by yourself, and you should definitely learn how to repressurise a combi boiler if you don’t already know.

Some boilers can be tricky to repressurise but most are very simple.

What causes a Baxi boiler to lose pressure?

There are many causes for a Baxi boiler to lose pressure. The most common cause of a Baxi boiler losing pressure is a leak, this could be on the boiler or anywhere on the central heating system.

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 by. Or, the filling loop on the Baxi boiler 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.

You should ensure the heating is turned off before repressurising the boiler as it will sometimes fire up as soon as it reaches the minimum working pressure.

This can cause the pressure gauge to move around so you don’t get an accurate reading but it isn’t a big deal.

How do I increase the pressure on my Baxi boiler?

To increase the pressure on your Baxi boiler you must add water to the heating system using a filling loop.

The filling loop should be under the boiler on a combi or could be elsewhere on the system if it’s not a combi.

You must open both valves on the filling loop (or one if it only has one) to increase the pressure then close both valves when it reaches 1 bar on the pressure gauge.