How to bleed radiators with a combi boiler

Combi boilers come with a lot of useful benefits for homeowners thanks to their compact design that heats water on demand instead of requiring a storage tank. You might think that this will negate the need to bleed your radiators like you would with a conventional boiler but unfortunately this is not the case. 

If you’re noticing that your radiators aren’t warming up properly, you’ll need to bleed the radiators to release the trapped air. In this guide, we’ll be exploring how you can bleed your radiators with a combi boiler, so you can always make sure that they’re working effectively when you need them. 

Why do you need to bleed your radiators?

There are a number of reasons why you might need to bleed your radiators, as mentioned above sometimes they can take longer than normal to heat up. Also, if the system is making strange noises or the radiator is hot at the bottom but cold at the top, these are other signs that your radiators require bleeding. 

Despite the key benefit of combi boilers providing water to your taps and showers at the same pressure as the mains, if you have trapped air in your radiators, it can cause too much pressure to build in your central heating system. As a result, your entire heating system can be left inefficient with hot water not being able to circulate as it’s meant to. Not only will this mean your home can take significantly longer to heat up than it should, but also it will be working harder and using more energy, leading to steep increases in your energy bills. 

When should you bleed your radiators?

You can bleed your radiators at any time of the year, especially if you are noticing any of the symptoms above. However, a lot of homeowners will bleed their radiators near the beginning of winter as the slightly colder temperatures will help you notice whether they are working properly or not. If you want to check the pressure in your system to determine whether you should bleed your radiators, look at the front of your combi boiler. 

There should be a gauge indicating the level of pressure that is in your system. The reading will be most accurate when the heating, taps, and shower are off, and it should be around 1.5 bar. If the pressure reading is higher than this, you will need to bleed your radiators to release some air and bring the pressure down to within a normal range. 

Steps for bleeding your radiators with a combi boiler

Turn the combi boiler on and up to the highest setting 

Wait until all your radiators are on and fully heated then check for signs of trapped air in any of them. 

Check for anything out of the ordinary 

If they start to feel cold anywhere or you hear unusual noises, note down where it is coming from, as these will be the radiators that require bleeding. 

Turn off the boiler 

Once you know which radiators need to be bled, you can turn off the boiler and wait for it to go completely cold before you start bleeding. This is because if you don’t you will end up with a stream of very hot water pouring out of the radiators, which is a serious burn risk to you and can make a lot of mess. 

Prepare the area for bleeding 

Locate your radiator bleed valve, which should be on the top or at the side of the radiator. Slot your radiator key into the valve and put a container underneath the valve. If you’re going to bleed multiple radiators, you should start with the one that is furthest away from your boiler and move closer to it as you go. 

Start bleeding the radiators 

Rotate the valve counter clockwise using the radiator bleed key or some other tool you have available in order to begin draining the radiator. A quarter to a half turn should be enough, but you will know if it is starting to bleed if you hear a hissing sound and air escaping. 

Close the valve when complete 

Use a cloth to secure a strong grip of the key and valve and to ensure water doesn’t spray out from the valve. When the water starts to reduce to a steady trickle, all the air from the radiator has been released and you should turn the key clockwise to close the valve. If any water has dripped down the radiator itself, make sure to wipe that off to prevent the risk of rusting. Repeat the process with all the radiators. 

Turn the heating back on 

When you bled all the radiators that needed it, turn your heating on again and check for cold areas or unexpected noises. If you’re still noticing some problems, you might need to bleed certain radiators again. 

Check the pressure gauge 

Combi boilers can lose pressure when you bleed the radiators, which means your gauge might show a reading off less than 1. If that’s the case, you will need to repressurise the system to get the pressure back up to normal. 

Where can I find combi boiler spare parts?

Bleeding your radiators is a good solution if you are noticing problems with your combi boiler system. However, if you have followed the steps above and are still experiencing issues you might want to contact an engineer who can check for what might be causing them. 

If it is confirmed that part of your boiler isn’t working as it should be, you can find high quality, affordable UK boiler parts at NBS. As experienced boiler spare parts suppliers, we offer a wide range of boiler parts from many brands so you’re sure to find the exact part you need with us. Explore our online shop today.