Boiler Loses Pressure, Does Your Boiler Suffer In This Way?

Boiler Pressure Loss On Guage

You get home from work on an icy winter’s day, chilled to the bone. Before you even take off your shoes or thick winter coat, you switch on your heating to warm up the house only to find that the boiler loses pressure.

Not only is the boiler’s pressure gauge showing that the pressure is low but if you have a combi boiler then your radiators are struggling to throw out the heat that they used to, which is horrible news for anybody; even worse if you’ve got elderly or sick family members or very young children in your household.

You also notice that your water pressure is down on your taps and taking a shower is now becoming a daily chore rather than a pleasure with a trickle of water rather than the refreshing jet of water you are used to.

Maybe you have a look online or speak to some people you know to see if there is something you can do to sort out the problem, and you find out about re-pressurising the boiler.

This can be done relatively easily – usually your boiler will have a tap which allows you to manually increase the pressure by adding water to the system.

If you have a Baxi Back Boiler Losing Pressure then read this.

Is Your Combi Boiler Loosing Pressure?

You should see the pressure gauge start to rise and the pressure on a combi should usually hold steady at around 1.5 bar. (Please always remember to refer to your boiler manual for specific instructions and to find out the correct pressure for your boiler).

Top tip from ADI: water expands when hot (increasing the pressure slightly) and contracts when cold (decreasing the pressure slightly), so a small amount of fluctuation on the gauge is normal.

Observation of the pressure gauge should be carried out when the temperature of the water in the system is cold to eliminate any variation in pressure due to change in temperature.

Generally, the pressure should be somewhere between these two points shown in image A and B:


Boiler Loosing Pressure at 1 bar



Boiler Not Loosing Pressure at 1.9 bar


If it’s pretty much holding steady between either of these points, you should have nothing to worry about. However if it’s falling from either of these two positions down to the red zone on the left, then the problem will need some attention.

You’ll also have a problem if it rises up into the red zone on the right, but that takes us in to a different topic of expansion vessels and pressure relief valves.

Here’s an example of a digital pressure gauge holding steady at a healthy 1.6 bar:

Digital Boiler Pressure Gauge 1.6 bar

Re-pressuring the boiler is likely to only be a temporary fix and you really need to investigate the root of the problem. This will either a problem on the boiler itself – and some or all of its parts might need replacing – or it will be a leak on the central heating system pipework somewhere.

You can carry out visual inspection of your radiators, checking for signs of leakage such as rust, damp patches or water around the radiators or on your floors or walls. If you identify anything above ground, you might be able to see if a local plumber can fix the problem.

Be sure to read our complete guide to boiler pressure loss – we are sure you will find it helpful.

However if you have any doubts, if you have multiple damp patches, or if you find nothing at all, you’ll probably want to contact ADI on 0800 731 3843 and have one of our Engineers perform a non-invasive leak detection on your underground pipework, which is the fastest and most cost-effective way of finding the source of your leak.

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