Kingston Plumbing

Bleeding Radiators

Cold spots with radiators are a very common issue in heating systems. Cold spots can occur for a number of reasons, 1 being air trapped in the system (top of the radiators are cold), and another being ‘sludge’ in the radiator (bottom of the radiators are cold).


How Does Air Become Trapped In Radiators?

Air becomes available in heating systems from sludge or when filling your heating system. When you first fill your heating system with cold mains water through the filling loop, all the air that is naturally stored in the pipework and radiators is pushed to the top of the radiator.

The build up of sludge in radiators and systems is due to corrosion. Corrosion happens when air and water is mixed (oxidisation/rust), so preventative measures must be taken to stop corrosion. To do that, you must get rid of any air in the system as soon as possible. Oxidisation/rust produces a gas called Nitrogen, with cold spots at the bottom of the radiator from the rust sludge, you now have cold spots at the top due to the air (Nitrogen gas).


Why Are Cold Spots On Radiators Bad?

All radiators have a heat output, calculated in BTU’s (British Thermo Units). BTU’s measure how efficient a radiator is and how much heat is emitted into the room. If a radiator has sludge and/or air trapped within itself, the heat output will be inefficient, thus causing your boiler to work harder and for longer, causing you to spend more of your hard earned money on the ever increasing gas prices!

Oxygen, causing sludge (rust), causing Nitrogen, will attack the steel radiator and cause pin holes. The water in your heating system can be very dirty, and if radiators start to pin hole, black water from the system will be spirting out all over your home! NOT GOOD! The pressure in your boiler will drop, and if it drops below 1Bar, you will not have any hot water.

All these problems, just from a little bit of air in your heating system…


Removing Air From Radiators

The removal of air from your heating system is a very easy simple job, that any homeowner and DIY’er can do! The only tools you require are: Radiator bleed key, Slotted screwdriver and an old rag or cloth (we use toilet/kitchen roll or blue roll). Air travels upwards. Usually, radiators on the ground floor are free from air, but it’s always best to vent all radiators on a system to ensure no air is present at all!

Firstly, ensure the boiler pressure is at 1.5Bar and open all of the TRVs (Thermostatic Radiator Valve) on your system. Starting from the lower radiators on the system (ground floor), locate the air vent on each radiator, they will be located at the top of the radiator, on the side panel. Some older radiators have small vents on the top-back which are a little harder to find. Using your radiator bleed key and old rag, insert the key into the vent, and turn anticlockwise (about half a turn, until you can hear the air or water dispersing ) whilst wrapping the rag around the vent to catch any water. Once the air has started venting from the radiator, get ready for the water. Once water has started releasing, close the vent using the key (turning clockwise). The release of water after the air has dispersed will mean that all of the air has been removed from that radiator. You must repeat this for each radiator in your home, again remembering to do this on all of the lower radiators, then work your way upstairs, removing air from the top floor radiators as your last step.

Now complete, you must check the boiler pressure once more as the release of air and water will have dropped the pressure. Top up the pressure using the filling loop to 1 – 1.5Bar.


Fire up your heating, wait for the radiators to get hot, ensuring all radiators do get hot and check for cold spots at the top of your radiators, if a radiator has cold spots, re-vent that particular radiator, remembering to up the pressure in the boiler, if required.


Kingston Plumbing are proud to supply Hull and Surrounding areas with your local affordable plumber, we pride ourselves on our premium workmanship and brilliant customer service.

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