BOILER LOSING PRESSURE? WHAT CAUSES IT AND HOW TO FIX IT.

Loss of pressure on your boiler or heating system has only one cause: you have a leak.

The regularity of the pressure loss indicates the size of the leak. If you’re topping your pressure up hourly, the leak is significant. If it’s only every few weeks, it’s minimal.
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You can increase the pressure yourself on your boiler or heating system. But, if you have to do this regularly, there’s a problem that needs attention.

​A pressurised heating system has to be maintained at between 1-1.5 bar. If the pressure drops too low, it affects the performance of your heating.

​How do I know if I have low pressure?

You may find any of the following symptoms:

• The radiators don’t heat up properly: perhaps they are cold at the top, don’t heat up at all, or they are cooler than usual.
• The system may become louder as your heating pump may be struggling to circulate water effectively.
• The boiler may lock itself out and display a fault code.
• You may notice the boiler turning itself off and on more often than usual. This is called cycling and is caused by poor water flow through the boiler’s heat exchanger.

​How do I check my pressure?

There will be pressure gauge on your system. This will most likely be on your boiler or in your airing cupboard.​

Most boilers have an analogue gauge like the one shown in the picture. Other’s display their pressure on a digital display on the front of the boiler.

In this video we demonstrate how to put more pressure into your heating system using the filling taps below the boiler.

The pressure should sit between 1 – 1.5 bar. If the pressure falls below 1 bar, it needs topping up. If the pressure has risen above 2 bar, that’s a different issue that needs looking at.

​How do I top up the pressure?

The pressure is increased by putting water from your mains cold water pipe into the heating circuit. This is done from a filling device that will usually be in the airing cupboard or just below your boiler.

Combi boilers tend to have built-in filling devices. You should find the taps below the boiler on the right-hand side. There will be two taps that need to be gently opened up until the pressure returns to a normal level.

Each boiler has its own type of filling device. Check out our help videos for your boiler manufacturer: Ideal and Baxi/Potterton

On a system with a hot water cylinder, you’ll most likely find the filling loop in the airing cupboard. This will be a flexible braided silver hose between two valves that both need to be opened to pass mains water into the heating system.

​How often should I have to re-pressurise?

Once or twice a year is about normal. If you’re doing it more often than this, especially during the winter months, when your heating is getting used often, then the boiler may need attention.

If you have to re-pressurise your boiler every day during the winter months, you probably have a deflated expansion vessel.

The pressure in your heating is regulated by a tank of compressed air somewhere on the system. Just like a car tyre, this needs regularly checking for the correct pressure. If the expansion vessel is empty, the pressure in your heating will start to fluctuate.

The pressure will rise as the water heats. If it gets to 3 bar, a safety valve opens, dumping pressure to a safe location. Once the water cools and contracts, the pressure will drop as low as 0 bar.
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Continuing to top your pressure up without dealing with the fault will cause damage to your system. Constantly adding fresh, oxygenated water into radiators will cause rust and corrosion. Get the help of a heating engineer as soon as possible if you are experiencing this problem.

​How do I find a leak?

Usually, a leak is easy to find. Stains on carpets of flooring will be an obvious sign. There may be a leak on one of your radiators or the valves that connect to it.

Before calling a heating engineer, check all the radiators in your house for signs of rust or staining. Look under and around your boiler to see if there are any connections becoming scaled or grimy.

It’s also worth checking outside your house for the pressure-relief pipe. If this is dripping it could go unnoticed, especially if it’s located somewhere inconspicuous.

Components inside the boiler that commonly leak are the pressure relief valve or automatic air vent. These can be easily changed by a qualified heating engineer.

In some case the leak is on the heating pipework. This may be visible pipework leading to radiators, or hidden behind walls or above ceilings.
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When heating pipework runs under solid floors, this can be expensive and very disruptive to repair. Your heating engineer may advise you to seek advice from a specialist leak detection company and to consult your insurance company.

​How can I fix a leak?

If the leak is small and inaccessible, your heating engineer may recommend adding a leak sealing solution, such as Fernox F4, into the system. This uses a chemical to seal pinholes in the heating pipework without causing blockages.

When the leak is visible it can be repaired by replacing the faulty component. This might mean replacing a radiator valve, a boiler component, or renewing a section of your heating pipework.

It’s a good idea to seek help from your local reputable heating company before the problem gets worse.

​Need help finding your leak?

Can’t find the leak on your system or struggling to get the help you need to fix it?

Ask your question in the box below and we’ll get back to you with our advice.