Last updated on September 23rd, 2023
An airlock in a radiator pipe can cause a radiator to not heat up or a radiator to be cold at the bottom.
Airlocked radiators are annoying and will cause rooms to be cold.
I have been a full-time heating engineer for over a decade and have cleared many airlocks without ever using a hose or removing a radiator.
Here I’ll show how I remove airlocks from radiator pipes the first time and every time.
Do You Have Airlocked Radiators?
A radiator not working is definitely a radiator airlock symptom but an airlock is not the only possible cause.
Here are some other causes of a radiator that doesn’t work:
- The radiator valve is turned off, blocked, stuck or broken
- The thermostatic radiator valve is on the wrong side (only on certain old TRVs as new ones are bi-directional)
- The radiator needs bleeding
- The radiators need to be balanced
- The radiator is not piped up correctly under the floor (only on a new radiator installation)
- The designer radiator flow pipe is on the wrong side (certain new tall radiators have to have the flow pipe going into a specific side of the radiator)
How to Clear an Airlock in a Central Heating System
If you have just drained the central heating system, it’s almost certainly an airlock causing the radiator to not heat up.
Here’s how I clear an airlock in a central heating system:
- Turn the heating on
- Close one valve (TRV or lockshield) on every radiator apart from the radiator(s) not getting hot
- Wait for the airlocked radiator(s) to get hot
- Bleed the radiator that is now hot
- Open every radiator valve
If you have more than one radiator airlocked and only one becomes hot after closing the valves, close a valve on the airlocked radiator that is now hot and wait for the other radiators to get hot.
How to Close Radiator Valves
You must turn off the radiators by closing one of the valves:
Thermostatic Radiator Valves
Turn the head on the valve clockwise until it’s on zero or off.
Turn the lockshield radiator valve clockwise as far as it will turn.
You can turn some lockshield valves with your hand, but for some valves, you will need to remove the cap and turn the spindle.
To turn the spindle, you can use:
Radiator Still Not Heating Up?
If after closing all the valves on the hot radiators, the cold radiators are still not heating up, then it will not be an airlock causing the problem you have.
How to Remove Airlock From Gravity-fed System
Having air trapped in a gravity-fed central heating system can be a nightmare.
An airlock in a gravity-fed system can cause the boiler to overheat and keep cutting out.
If you have problems with a radiator or two not heating up there you can follow the process above, but if the boiler is not firing up or cutting out, you will need to remove all the air.
Removing the air can take all day as hardly anything comes out, you have to just keep plodding on.
Here’s how I do it:
- Turn the heating on
- Bleed the radiators
- Bleed the bleed valve (typically in the hot water cylinder cupboard)
- Bleed the central heating pump
- Repeat, repeat, repeat until the boiler stays fired up
You must turn off the valves on the hot radiators forces the heat to the cold radiators and the full force of the central heating pump will go to where the airlock is.
This will force the air out of the radiator pipes and into the top of the radiator which can be bled out if needed.
I get airlocks regularly after draining and refilling central heating systems, and this method gets rid of the trapped air every single time.
If it doesn’t, then it won’t be an airlock problem you have.
Feel free to leave feedback or ask me any questions in the comment section below and I’ll try my best to help.
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Airlock in Radiator Pipes FAQs
Will an airlock clear itself?
It’s possible over time for an airlock in a radiator pipe to clear itself but it’s not very likely.
What causes an airlock in a radiator?
Air trapped in a pipe causes an airlock in a radiator, typically after draining and refilling a central heating system.