Water pressure hints and tips

Every boiler and central heating system needs a bit of attention occasionally, in addition to its normal annual service.

This includes repressurising the system and bleeding the radiators.  Your boiler's user guide has details on how to carry out these simple procedures, and you can find an overview and links to our How-to videos on this page.

If you still can't get your boiler to light, or you need help with the system and controls, please contact your installer or Baxi Customer Support for help.

Frequently asked questions

How do I find out what the pressure of my central heating is?

Combi and system boilers will have a pressure gauge in the control panel that looks like this:

Heat only (or regular) boilers installed on a pressurised system will have a pressure gauge installed in the pipework.

Open vented central heating systems (you will have feed and expansion tanks in the loft) are not pressurised and will not have a pressure gauge.

What should the water pressure be?

The normal operating water pressure for the central heating system is between 1.0 and 2.0 bar.

How can I increase the water pressure?


If the water pressure drops below 1.0 bar you need to repressurise your central heating system.  This is a simple maintenance job that you should be able to do yourself quite easily, and is best done when the system is cold.

Check out our handy How-to videos that show you how to repressurise your boiler, whether you have a rigid filling loop or a flexible filling loop.

1. The filling loop will be on the boiler itself or on pipework near to the boiler. The filling loop consists of two taps and a separate copper pipe with connection fittings.  When pressuring the boiler, connect the copper pipe between the two taps and make sure the nuts are tightened onto the taps.

2. Fully open on of the taps first, then, while watching the pressure gauge, carefully open the other tap.

3. When the needle on the gauge is between 1.0 and 2.0 bar, turn both taps off.


4. Disconnect the copper pipe from the taps and remove it.  Keep it in a safe place for future use.

Why do I need to add pressure?

The water in the central heating system needs to be at a certain pressure in order for the boiler to work properly and safely. There is a pressure sensor inside the boiler, and if the pressure is too low, it will switch off the boiler to stop it working without enough water and overheating.

What causes the pressure to drop?

Over time it is not unusual for the pressure to drop slightly.  However, if the pressure drops regularly, it could indicate that you have a leak somewhere in the central heating system.

How do I reduce the pressure in the system if it's too high?

If the pressure goes above 3.0 bar, the safety pressure valve in the boiler will operate and you may see water coming out of the pressure relief valve, which is usually on an outside wall where the boiler is installed. You can reduce the pressure by bleeding a radiator (find out how here) or draining some water out of the system using a drain point, usually found underneath a radiator:


How can I tell if the pressure is right or wrong?

The pressure gauge should have a reading of between 1.0 bar and 2.0 bar.  If the pressure drops too low, the boiler will stop working and show an error code.  For example, the error code for low pressure on the Baxi Duo-tec Combi is E119. You need to repressurise the system as described above. 

If the pressure goes above 3.0 bar, the safety pressure valve in the boiler will operate and you may see water coming out of the pressure relief valve, which is usually on an outside wall near where the boiler is installed.

Bleeding the radiators

If you have cold spots on your radiators, you have air in the system and need to bleed it.  We have a step by step guide to explain how to do it here.

Can I run a bath and shower at the same time?

If you have a hot water storage cylinder, usually found in the airing cupboard, you should be able to run a bath and have a shower at the same time, because you will have a store of available hot water.If you have a combi boiler, which heats the water as it is needed and doesn't have a hot water storage cylinder, and you open two taps, the boiler will split the water between them and you will get a reduced flow rate of hot water at both taps.

If you regularly need lots of hot water at the same time, it is worth considering having a system boiler, such as Baxi EcoBlue system and hot water storage cylinder, such as a MEGAFLO Eco, to ensure you always have enough hot water. Your installer can survey your home and advise the best boiler to suit your needs.

Information & advice

Our series of FAQs, technical advice articles and 'How to...' videos are designed to help you understand your boiler, provide helpful tips and even save you money.

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