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Boiler losing pressure? Causes of low boiler pressure & how to fix them

Here, we'll outline the common reasons for a boiler that's losing pressure, what's (probably) causing it, and how you can (try to) fix or repressurise it.

Boilers have the good fortune never to lose their keys, wallet, bottle or mind. 

But they do lose pressure – which severely affects their performance. And thus, your homes heating and hot water.

So what can you do about low boiler pressure? And more importantly - what can you do about a boiler with a pressure that keeps dropping? 

First things first, you don't want to lose your hot water or heating, so it's a good time to determine whether you need to replace or repair your boiler, and to get an idea of how much a new boiler may cost - you can check the latest prices here

What the hell is boiler pressure and why do you need boiler pressure?

Boiler pressure is simply the balance of water and air within your boilers sealed system.

Boiler Ying Yang

In order to function correctly, your boiler needs a particular balance of water and air to ensure the pressure in the system is adequate for when water is demanded from the boiler – essentially when you switch on your heating or hot water.

Too little pressure (not enough water within the sealed system) will result in an inadequate flow of water to heat your radiators or water.

Too much boiler pressure and the water will pass through the system like a Vindaloo to an uninitiated westerner.

Remember the universal balance that Thanos was trying to deliver through way of murdering half of all living beings in Marvel’s Avengers? Same thing.


Did you know if your boiler pressure keeps dropping, it may be a sign of a more serious problem? Find out what here.

If your boiler has been giving low-pressure readings on an all too regular basis, is over 10 years old and has seen better days, you may want to consider a replacement.

Does boiler pressure keep dropping? 

Your boiler losing pressure is an occurrence more natural than childbirth, and overtime (or, sometimes overnight) – they’re bound to lose some water (pressure) and require topping up (or, repressurised).

So if this is your boilers first rodeo – relax.

However, if your boiler pressure keeps dropping, it may be a sign of a more serious problem? Find out what here.

And just top up the pressure (we’ll tell you how, further down).

Boiler Pressure Gauge

You can identify if your boiler has lost pressure with a quick glance at the boiler pressure gauge on the front of your boiler cover.

What should my boiler's pressure gauge read?

When your boiler is switched off, the pressure gauge should read around 1 Bar – in the green zone on the gauge.

When it is in operation (demanding heat/hot water), it's pressure will increase slightly, then it should drop back down.

Need help? Here are our quick help guides:

How to top-up (repressurise) your boiler

In most cases, boiler pressure (if it's too low) can be resurrected at home really easily, in just a few seconds.

Step 1 - Find your filling loop

Boiler Pressure Filling Loop

Directly underneath your gas boiler should be some pipework, amongst which will be your filling loop.

The filling loop is the silver flexi pipe with either one, or two black (usually) taps on.

Step 2 - Increase the pressure

Top Up Boiler Pressure

To increase the pressure, you’ll need to open your one (or two) taps, full until they lock at 45 degrees. As you’re doing this, you should see the pressure rise on the boilers pressure gauge to around 1 bar. Ta-da, your boiler has been repressurised.

Step 3 - When you're in the green, close the taps

Fix Low Boiler Pressure

Once it’s back in that oh so reassuring green zone – close the taps again – ensuring they’re fully closed back to their original position.

Accidently leaving them open would put your boiler under more pressure than Theresa May is to deliver a hard Brexit.

Boiler keeps losing pressure, even after being repressurised?

If your boiler is losing pressure quicker, and more regularly than Manchester UTD lost league places after the departure of Sir Alex Ferguson, then something is not quite right.

Could the pressure dropping be a sign of something more serious that may warrant a new boiler? Read our quick guide on how to tell if your boiler needs replacing here.

And if you're just curious to see how much a new boiler will cost complete this quick questionnaire to find out for free.

The most common causes if your boiler is constantly losing pressure….

#1 - A leak in the system

Low Boiler Pressure From System Leak

A leak somewhere in your heating system may well be tricky to spot. The leak could be anywhere throughout pipework in your home, potentially spanning a large area.

It could well be a leaking pipe within a wall or under a floorboard. 

How to identify a leak in the system

Trace the pipework throughout your house where possible, checking for any signs of leakage. Particularly check around the joints and bends of the pipes – this is where seals are most likely to weaken over time and allow water to escape resulting in the pesky pressure loss that has you following pipes like a lunatic.

Have you had a boiler quote yet? Use our calculator to get an instant new boiler quote. 

How to fix a system leak

Leaks in your system, particularly harder to reach ones are something that you should leave to the professionals. You’ll need a Gas Safe engineer to reseal or potentially re-pipe your system where necessary. 

Curious to know which boiler brand performed worst? Find out in our report of the worst boilers

Boiler over 10-years old?

If your boiler is getting into or beyond its twilight years, strongly consider the potential repair costs of your system leak against the cost of a new boiler. System leaks caused by corrosion overtime or excessive limescale build-up could indicate a boiler that’s going to start racking up repair costs. A power flush can also help deal with the buildup of sludge and rust. 

Learn all about combi boilers in our what is a combi boiler guide. 

#2 - Leak in the boiler

Low Pressure Boiler Leak

Leaks from your system are most common, but components within the boiler leaking – usually due to age and corrosion – are not far behind as a leading cause.

Check our quick guide on how to identify a leak in your boiler.

If you’re comfortable, you could remove the cover from your boiler and carefully look for signs of water. However, we’d recommend leaving this to a Gas Safe engineer.

Is your boiler making a lot of noise? Find out why in our noisy boiler guide. 

How to fix a leak in your boiler

Again, this is going to require the services of a qualified heating engineer. They’ll need to identify which component of your boiler is leaking – with several of the components potentially being the culprit.

Worst case scenario here is probably a leak in your boilers heat exchanger. This is going to require a whole new heat exchanger costing several hundreds of pounds if of course, your boiler's manufacturer is still producing the correct parts for the model which is unlikely if your boiler is over 10-years old.

Repair or replace?

A leak in your boiler could still be a trivial problem that’s repaired cheaply, in which case a repair would certainly be preferred over a whole new boiler.

Depending on the component with the leak, however, combined with the age of the boiler – it could likely be more economical to consider a new boiler, with a long warranty.


#3 - Faulty part or safety device in the boiler

Low Pressure From Faulty Boiler Part

How to identify a broken boiler part

Certain gifted people from a long line of witchcraft and wizardry are able to acutely sense issues with the internal components of their boiler.

Others will rely on fault codes displayed on the boilers monitor and the rest of us make do with summoning a qualified heating engineer. This is likely what you’re going to need to do, fault code or not. 

How to fix a broken boiler part

In most instances, the faulty component of your boiler is going to need to be removed and replaced by your heating engineer.

Prices for this will vary depending on the age of your boiler, availability of replacement parts and the broken part itself. A boilers heat exchanger, for instance, is going to set you back an alarming wedge.

The average boiler repair cost

Note: Thinking about an immersion heater instead? Read our guide to find out how they compare to combi boilers.

Still not sure which boiler is right for you? Check our guide all about the main types of boilers.


Is low boiler pressure dangerous? 

In most cases, low boiler pressure is nothing to be concerned about, but if you do have concerns you should always seek the advice of a registered Gas Safe Engineer. 

Typically, low boiler pressure means water can't be circulated around your system or delivered to your taps and showers. As a result, the boiler will usually turn off and display an error code to alert that you that there is an issue resulting in low pressure. 

Pressure dropping can happen to any boiler, even the most 'popular' brands. Here's the most common ones (with error codes).

Worcester Bosch boiler pressure loss

Worcester Bosch Boiler Losing Pressure

Error codes indicating Worcester Bosch boiler pressure loss:
E2, A1, CE 207, H07, 224 V, 1017W, 2970 B, 2971 B.

Pressure error codes applicable to: 
Worcester Bosch CDi Classic, Worcester Bosch CDi Highflow, Worcester Bosch CDi Compact, Worcester Bosch Greenstar 25i, Worcester Bosch Greenstar 30i combi, Worcester Bosch CDi Classic Regular.

Note: If your boiler's busted, check out our complete boiler replacement guide. 

Vaillant boiler pressure loss

Vaillant Boiler Losing Pressure

Error codes indicating Vaillant boiler pressure loss:
F.24, F.12, F.22, F.73, F.75

Pressure error codes applicable to:
Vaillant EcoTEC, Vaillant EcoPure, Vaillant EcoTEC Plus, Vaillant EcoTEC Plus Regular, Vaillant Turbomax Plus.

BAXI boiler pressure loss

BAXI Boiler Losing Pressure

Error codes indicating Baxi boiler losing pressure:
E28, E119, 118, 119, H.02 – 06, E.02 – 7, E118

Pressure error codes applicable to:
Baxi 600 combi, Baxi 200, Baxi 400, Baxi EcoBlue, Baxi EcoBlue Advance, Baxi DuoTec, Baxi Platinum

Ideal boiler pressure loss

Ideal Boiler Losing Pressure

Error codes indicating Ideal boiler losing pressure:
F1 or ‘Water Pressure’ description on display.

Pressure error codes applicable to: 
Ideal Logic, Ideal Logic Plus, Ideal Isar, Ideal Vogue, Ideal Vogue Max, Ideal Mini

3 key pressure takeaways

#1 - No leak? No problem

If there are no clear signs of a system or boiler leak – it’s always worth topping up your boiler pressure manually first – it’s easy, free and in most cases will do the job – the condom of boiler fixes.

#2 - Eat. Sleep. Leak. Repeat.

A boiler that’s relentlessly losing pressure is alluding to a more serious issue and one that shouldn’t be tackled by unqualified hands. Call a Gas Safe engineer, have them diagnose the problem and make a decision from this point.

#3 - How to know when its time to replace your boiler?

Boilers don’t last forever. It’s part of the philosophical conundrum that makes you love them when they’re working. There’s no good without bad and no hot water without cold.

But keeping your boiler on life support – constantly repairing it and pulling it back from the brink of death is costly, very costly.

So if you're not sure read our quick guide on deciding whether to fix or repair your boiler. 

In the meantime, here's what else you can do to prepare:

    • Check out reviews on your current boiler
    • Get quotes for the necessary repairs and consider the likelihood of that – or another issue – occurring again. If it’s over 10-years old, you’re on thin financial ice
    • Put some leg work in and read up on the best boiler to buy (to make sure you don't buy a wrong'un)
    • Check out which boiler brands are best to make sure you are buying from a reliable brand 
    • Weigh it up against the cost of a new boiler, covered for repairs under a 10-year warranty. 0% monthly options & Buy Now Pay Later available

If your boiler can be fixed easily and cheaply with little chance of a future breakdown, a repair is your best bet.

An old boiler, with an expensive repair required, is certainly worth taking the leap to a new boiler.


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