How to top up the water pressure in your boiler…
Are you feeling the pressure? Or more specifically, the lack of it?
If you’ve been experiencing boiler problems such as a lack of hot water; it could be that low pressure in your boiler is to blame.
This is because modern boilers require constant water pressure in order to function properly.
If your boiler is losing pressure, it will cause problems, such as the dreaded, no hot water, situation.
The good news is that low pressure is usually easy to spot. And, in some cases, you can address it yourself.
To help you stay calm under low pressure; here’s our handy guide to what low pressure is, and how to fix it.
What is the difference between water pressure and boiler pressure?
It’s easy to get confused between the terms boiler pressure and water pressure; but they actually refer to two different things.
Boiler pressure refers to the pressure of hot water running in your sealed central heating system; while water pressure is the pressure of the water coming through your taps.
What is boiler pressure and why does it matter?
Your gas central heating system works by heating cold water and pumping it around your pipes and radiators.
Older heating systems may have used a small storage cistern in the loft to supply water into the heating system.
But most modern (and some older) heating systems are sealed.
This means that there aren’t any vents to manage the water expanding and contracting as it heats and cools. Instead, the system is pressurised in order to ‘push’ the water around your system.
To work efficiently, your boiler must maintain a stable pressure; which is determined by the volume of water in your heating system.
What pressure should a boiler be at?
It’s important that your boiler pressure is just right.
Low boiler pressure can cause your system to cut out, preventing your central heating from working.
Alternatively, if there is high boiler pressure, the system will be strained beyond normal capacity and could potentially fail. Re-pressurising your boiler will help to keep your boiler working well.
Not all boilers will experience these difficulties though.
The Worcester Bosch Greenstar 8000 boasts an optional unique intelligent filling system. This new technology ensures that your system pressure is kept at its optimum level. Which is great if you’re sick of the problems associated with high or low boiler pressure.
The intelligent filling system monitors the boiler pressure and automatically maintains the system pressure at around 1.3bar; removing the need for you to manually top up the boiler pressure.
But if you don’t have this, read on!
What causes boiler pressure to drop?
Although the pressure gauge on your boiler will alert you to the fact you’re losing pressure; unfortunately, it can’t tell you why. There are several potential reasons why your boiler pressure keeps dropping:
Pressure drop caused by leaks
The main culprit for a loss of pressure, is that water is escaping from somewhere in your heating system. In other words, you have a leak.
This doesn’t necessarily mean that you’ll see water gushing out of a burst pipe; or you’re wading through a flood though.
A leak may well be tricky to spot. A tiny leak anywhere throughout the pipework in your home; which may be underneath a floorboard; could lead to a gradual drop in pressure if it’s gone unnoticed for some time.
You can trace the pipes around your home to look for signs of damp patches. Pay particular attention to the joints and bends of the pipes, where seals might have weakened over time.
Pressure drop caused by bleeding radiators
Another potential reason for a loss of pressure is if you’ve bled your radiators recently.
This is because boiler pressure relies on the perfect balance of air and water in the sealed system. When you bleed a radiator, air (and possibly some water) is released, which lowers the pressure in your boiler system.
After you’ve bled your radiators you should check the pressure gauge on your boiler.
If the pressure is correct, the needle gauge on your boiler will be facing green. If it’s on yellow then you will need to re-pressurise the system, using the steps outlined below.
Pressure drop caused by a faulty pressure relief valve (PRV)
Pressure relief valves, as their name suggests, are designed to prevent a buildup of pressure in your boiler.
The valve opens to release pressure when the level becomes too high; usually when the boiler exceeds 3 bars. And closes again when the pressure has dropped to within a safe range.
If this valve becomes faulty; it will start leaking water from the central heating system; which can cause a drop of pressure.
You can check for this by looking for a small copper pipe exiting your property; which is usually close to the boiler or cylinder.
If this is dripping, you need to call a Gas Safe engineer to change the valve.
Pressure drop caused by a damaged expansion vessel
Another potential cause of a loss of pressure is a faulty expansion vessel.
Expansion vessels act like a shock absorber; keeping the pressure in a combi boiler stable while water expands as it heats and contracts as it cools.
If this valve fails, your boiler pressure will rise to 3 bars when it heats up. The valve will then let out the pressure from the boiler, so it can return to a safe level. This will cause a significant drop in the pressure gauge.
During your annual service, your expansion valve will be re-pressurised, which will hopefully avert this problem.
What pressure should my boiler/heating system be at?
If you have a system or a combi boiler; it will usually have a pressure gauge built into the appliance itself. But you might be wondering what pressure it should be at.
As a rule of thumb, the normal boiler pressure is between 1.0 and 1.5 bars.
It’s normal for this pressure to increase slightly when the system gets hot. But if the pressure in your heating system is over 2.5 bar; you may already have a fault, or a fault might be developing.
How can I check my boiler pressure?
Checking your boiler pressure is very simple. The pressure gauge will usually be on the front part of your boiler.
If you have a digital gauge, you should see a flashing pressure reading, if there’s a low (or high) pressure warning.
If you have a hydraulic pressure gauge, the correct boiler pressure will be indicated with a green zone. And the maximum safe operating pressure with a red zone.
When the heating system is cool, the pressure should be between 1 and 1.5 bar on the pressure gauge; and the indicator needle should be in the green section.
If the pressure is below 0.5 bar, down in the red section; water has been lost from the system and must be replaced.
But if the pressure is too high, over 2.5 bars, the needle will be in the red section.
Where the pressure gauge indicates high pressure as a result of over-filling; you’ll need to bleed a radiator until the pressure gauge returns between 1 and 1.5 bar.
Can I fix low boiler pressure myself?
If the pressure in your heating system has fallen below 1 bar, it needs to be topped up.
Boiler pressure systems differ, so it’s always best to check your manual, to see if you can re-pressurise it yourself.
Re-pressurising your boiler means allowing more water to enter the system, from the water mains supply; through something called the filling loop. If in doubt, you should consult a professional.
What is a filling loop?
The filling loop is a small, braided hose with connections on either end.
It provides a temporary connection to the mains so that you’re able add additional water to your heating system.
Because the volume of your heating system is fixed, adding more water increases the pressure.
Filling loops can be either part of the boiler itself, or it can be fitted close by it. They are usually located on the underside of the boiler fixed to the pipework.
How long does it take to repressurise a boiler?
The whole process, including attaching the filling loop; opening and closing the valves; and removing the filling loop; should only take a couple of minutes.
Depending on how low the pressure of your boiler is; you should allow water in through the valves for around 10 seconds. If it takes longer than this, you could have a leak in the system.
Step-by-step – How to top up the water pressure in your boiler
To top up the water pressure in your boiler, follow these steps:
- Switch off your boiler and allow it to cool.
- Double-check that both ends of the filling loop are securely attached.
- Open both valves, to allow cold mains water into the system (you should hear it). To do this, turn the lever(s) or flat headed screws at either end of the flexible braided hose. The levers or screws should be turned individually. They will likely only turn a quarter of a rotation from the off to on position; and you should observe the pressure gauge while you are turning each one.
- Wait for the pressure gauge to read 1.5 bar
- Close both valves, one after the other. The lever/s (or screws) should then both be turned fully off again to prevent the system pressure from getting too high.
- Switch the boiler back on and, if needed, press the reset button.
- Undo both ends of the filling loop and remove.
If you accidentally overfill your heating system; you’ll need to reduce the pressure in your system by bleeding your radiators or calling in a professional.
Why won’t my boiler re-pressurise?
If your boiler pressure drops immediately after you’ve followed the steps above; this could indicate a leak somewhere in the system; or a damaged pressure relief valve.
If you’ve tried to re-pressurise the system once and it hasn’t worked, don’t keep trying it. At this stage, you should contact a heating engineer to have a look at what’s going on.
How often should I top up my boiler pressure?
Whatever the cause, your boiler shouldn’t be low on pressure all the time. If you’re having to top up your boiler more than twice a year; you need to call in a professional to get to the bottom of it.
If you have a leak; or a faulty boiler part; and you don’t get it fixed; the situation will get worse. And your boiler could suffer irreversible damage.
Not only that, repeatedly topping up your boiler allows in oxygen; which will encourage further corrosion and a buildup of sludge. If this happens, you will need a power flush to cleanse your system.
If you’re regularly having problems with pressure, now might be the time to consider a boiler upgrade.
Contact one of our friendly team at The Heating People, who can provide you with tailored advice.