How to Repressurise Baxi Boiler Pressure

Last updated on October 15th, 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.

Pressure Too Low

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

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.

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.

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.

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

• 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.

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.

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.

Leak

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.

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.

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.

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

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 Guides

• Baxi boiler no hot water
• Replace pressure relief valve on a Baxi boiler
• Baxi E119 fault code repair
• Baxi E133 fault code repair
• Baxi boiler is not firing up

Summary

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 any questions in the comments below, and I’ll do my best to help. If you found this post helpful, please consider sharing it.

FAQs

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.