How to repressurise a boiler
16 November 2023
The purpose of the following advice is to provide useful tips for our Customers and is not designed to replace professional advice. It does not necessarily deal with every aspect of a topic and if you are in any doubt, you should consult a qualified expert for their help. You should never attempt to carry out any activity which may put you or others at risk or which may cause damage to your or anyone else's property and the activities described must not be attempted by anyone under the age of 18.
Always read any manuals and safety instructions alongside the advice.
Just like most appliances in the home, boilers need some attention every now and again to keep running at their best. One common problem that many people experience, especially if their boiler hasn’t been running much recently, is low boiler pressure. This can cause a few issues in the home and may even cost you more because it can cause higher energy bills.
Find out how to spot the problem, what problems it might cause and how to repressurise a boiler by following our guide.
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Is low boiler pressure dangerous?
Low boiler pressure, in itself, isn’t dangerous, but it can mean that your heating and hot water don’t work as they should. This may mean that you have difficulty heating your home to an adequate temperature, which could potentially be dangerous if there are vulnerable people living in the home and it’s very cold.
Low boiler pressure that happens persistently or suddenly can also be a sign that there might be a leak somewhere within your home, which can cause damage to the home if it isn’t found quickly, or can potentially be dangerous if it comes into contact with electrics or electronic devices.
If you think that there could be a water leak in your home, you can take a look at our guide on what to do if your home floods because of a leak.
The main issue with having low boiler pressure is that your boiler has to work much harder to try and heat your home and hot water to the right level, which will cost you more in energy use than it would if the pressure in your boiler was in the correct range.
You might notice that your radiators aren’t getting as hot as they usually would, or that your hot water takes longer to run warm and isn’t as hot as you’re used to. These can both be indicators that you might have low boiler pressure.
There can also be other reasons why your radiators aren’t heating up.
How to check your boiler pressure
The easiest way to determine if your boiler is suffering from low pressure is by examining the water pressure gauge. If you’re not sure where to find this then refer to your boiler manual, which usually has a diagram indicating the boiler’s various controls.
Your boiler will have either a hydraulic or digital gauge. With a hydraulic gauge, your boiler’s pressure is represented on a dial, with red areas to show both low and high pressure. If your boiler’s water pressure is low then the indicator needle will be pointing to the red ‘low pressure’ area on the left side of the dial.
With a digital gauge, the water pressure is shown in bars. When your water pressure is low, your reading will drop to below one bar and may flash intermittently or be accompanied by a pressure warning.
What's the right water pressure for a boiler?
Your boiler’s ideal water pressure reading is anything between one and two bars. When your reading drops to below one bar then your pressure has become too low whereas a reading above 2.75 means your boiler’s pressure is too high.
Repressurising a boiler with high pressure can be hazardous and should only be carried out by a qualified heating engineer. If you’re a Places for People customer in a managed property, get in touch with us and one of our experienced engineers will come out to take a look.
Please note: a water pressure reading of one bar is normal when your heating is turned off.
What causes low water pressure?
Heating system leaks
One cause of low boiler pressure is a leak in your central heating system, with minor leaks accounting for gradual drops in water pressure.
Check for damp patches near your boiler, radiators and pipes. If you find any and you’re a Places for People customer, contact us and we’ll arrange for an engineer to come out and fix the leak. If you’re not one of our customers, you can arrange for a qualified professional to come out instead.
If you aren’t able to find a leak and you’re still experiencing low water pressure, one of our engineers can still come out to you to find out what the problem is. That might involve inspecting the inside of your boiler for leaks, which is a job best left to the experts!
Radiator bleeding
Low boiler pressure can also occur after bleeding your radiators. Releasing air or water from your heating system while bleeding radiators can sometimes result in pressure loss.
Take a look at our guide on how to bleed a radiator properly.
In the following steps, we’ll show you how to restore your boiler’s low water pressure back to normal without having to call out an engineer.
How to repressurise my boiler
To start with, spend some time reading the manufacturer’s instructions since this will help to familiarise you with your boiler’s setup and the best course of action. It’s also worth checking online for instructional videos that relate to your particular boiler’s model, which will provide a visual guide to the repressuring process.
The basic steps to repressurising a filling loop boiler
1. Turn your boiler off and wait for it to cool down.
2. Make sure that both ends of the filling loop are firmly in place.
3. Open both valves and keep them open until your boiler’s pressure reaches 1.5 on the gauge. Note - as this happens, you will hear the mains cold water running into the system.
4. Once the correct pressure is reached, close one valve first and then the other.
5. Turn your boiler back on and press the reset button if needed.
If you have a repressure key
1. Turn your boiler off and wait for it to cool down.
2. Look beneath the boiler to find the concealed tray containing the repressure key and corresponding slot.
3. Making sure it aligns with the ‘open padlock’ sign, position the key into the slot then push it firmly in and towards the ‘closed padlock’ sign.
4. Locate the white square nut and slowly turn it clockwise until the pressure on your gauge increases to 1.5 bars. As you do this, you will hear water flowing into your boiler.
5. Continue to turn the nut clockwise until the water has stopped flowing.
6. Return the key to the ‘open padlock’ position and if a small amount of water escapes don’t be alarmed – this is perfectly normal.
7. Switch your boiler on again.
What if the boiler pressure keeps dropping?
If your boiler pressure is dropping regularly, it’s possible that there is a leak in the heating system with the potential to cause water damage to your home. If this happens, and you are a Places for People customer, contact us and we will arrange for someone to come and fix the issue.
In conclusion
We hope you found this information useful. Remember, if you’re still having issues with a managed property, you can contact Places for People.
If you are not a Places for People customer, we do recommend using a reputable website to find a suitable tradesperson such as Checkatrade, TrustMark or Trust a Trader.
In the meantime, why not check out some of our other how-to-guides and insightful blogs?