How To Bleed Your Radiators And Improve Central Heating Efficiency

How To Bleed Your Radiators And Improve Efficiency.

If there is a lot of air in your radiators, then the hot water flowing around your central heating system cannot do its job and heat up each radiator in your house, and therefore heat your house efficiently, or effectively.

There are several reasons why air gets into the system, such as

Leaks from the system radiators, boiler or pipework
Maintenance work causing air to enter the system.
Airlocks caused by this maintenance work.
Corrosion inside the system releasing hydrogen and other gasses into the radiators.

This is corrosion from the metalwork inside the system due to the “normal” tap water corroding it and added chemicals in the water not helping, as well as limescale and other reactive agents in it.

Before I go on; I recommend adding Fernox for copper tubular boilers (modern, and combination boilers), (Or if your system is very old; use “Fernox” for Cast Iron Systems, if applicable).

Please click to enlarge pictures, especially the ones lower down showing the radiators and the boiler itself.

Fernox Corrosion Inhibitor

I Highly recommend the latest “Fernox” corrosion inhibitor, or its equivalent; I installed it in my parents’ system in 1988, and mine in 1997, and to be honest I have NEVER had to bleed the radiators since the systems have been installed thanks to the inhibitor doing it’s job!

Moreover; I extracted some water from both systems as an experiment, and put them in a jar with a steel nail and diluted them 50% with tap water and the nails didn’t go rusty! Brilliant stuff, and highly recommended!

The illustration below isn’t mine; but it shows exactly the results that I got!

Corrosion-Inhibitor-Nail-Test-Fernox

OK then… on to the simple job of bleeding your radiators, but a few notes first to clarify some side points…

In the case of a sealed system, (that is one without a header tank in the loft with a ball cock (ball valve), like inside a toilet tank when the lid is removed; it is illustrated below, but it shows it also as a cold water tank in this case)

Old Type System With Header Tank

What you will generally see in your loft or the upper part of your airing cupboard would usually look more like this if you have a non-pressurised system. This means usually no pressure gauge will be fitted, or if there is one, it will not register any pressure, showing that the system is “open vented”…

Open Vented Central Heating Header Tank

Just a side point… If you have a “header tank” and it isn’t refilling, the ball valve may be stuck, and the tank empty. I went to see a local woman’s heating system, and her radiators upstairs were totally empty because the ball valve in the tank had rusted and stuck. The water had evaporated from the tank and the system, as there were no leaks at all when I had repaired it! When I opened up a radiator bleed screw; nothing happened. I greased the pivot point on the ball valve, and it then worked OK until she had a new system fitted 10 years later!

I also added “Fernox” directly to the header tank od her system; but in the case of a sealed system you can inject it directly into a radiator with a syringe directly into a bleed point on the radiator. Add 1/3 of the bottle to the tank, and inject the rest into a radiator if you have a header tank. If you have a sealed system inject it directly into a radiator once you have reduced the pressure by opening a bleed valve and draining some water off. Do not overfill the system!

Fernox-water-treatment-injector

Check that there is sufficient water in the system on the pressure gauge. It usually reads above 1 Bar, or around 15 PSI (pounds per square inch); in use the gauge may go up to 1.5 Bar or just over 20 PSI. It should also be over or above the red marker as shown below. (Glow Worm Swift-Flow 80 Combi boiler shown for this illustration)

Check Pressure Gauge

If you are running your heating feel the radiators to see how hot they are getting on the very top…

Run The Heating And Feel If The Top Of The Radiator Is Colder Than Lower Down

Feel the radiator lower down too to see if there is any difference…

Is The Middle Of the Radiator As Warm?

And check the bottom of the radiator to see how warm it compares to the middle and the top (once they have fully warmed up after 10-15 Min’s or so of course!)

Is it Warmer Here On The Radiator?

If there isn’t much difference they may be OK or 95% full, so it does not hurt to check; but if the top is very much colder than the bottom; this indicates that bleeding is required, and also that you should be checking for corrosion and leaks possibly, especially if it is really different, such as only half full of water, which would only heat half of the radiator up!

This is or course assuming the radiator is fully turned on, and that TRV’s (thermostatic radiator valves) are not seized, and that they are also fully on! It also assumes that your radiators are balanced (even all around the house), and that the radiator is getting a good flow of hot water. (Check this out to be sure first)

Next get your radiator key. Steel or brass keys are the best; cheap alloy or aluminium ones will break, strip, or round out. (I have found this out myself!)

A Good Quality Radiator Key

This shows the square end for the radiator bleed screw…

A Typical Brass Radiator Key; Aluminium or Alloy Ones Break; Brass Or Steel Ones Ar Better

A Typical Brass Radiator Key; Aluminium or Alloy Ones Break; Brass Or Steel Ones Are Better

Locate the radiator bleed screw on the top end of the radiator (double panel radiators will have two of these, unless they are physically joined together at the top which is usually the case for most modern radiators)…

Locate The Radiator Bleed Screw (Myson Round Top Radiator Example)

Check that the bleed screw looks OK, and isn’t rounded or damaged, remove any debris if any is present, and it may pay to give it a short squirt of penetrating oil, or WD40 if it looks or is stubborn. If the bleed screw is damaged then you may have to try a pair of long-nose-pliers to get a grip on it, but this is not the usual thing to do, and is only 50/50 at best in it’s success rate at undoing the screw. It also chews up the radiator bleed screw more, making future maintenance more difficult.

Insert the radiator key fully and firmly over the radiator bleed screw; you will feel it is solid and not spinning if it is fully home over the screw to avoid damaging it by stripping the head or the key.

Place Key Onto The Radiator Bleed Screw Firmly; Ensure A Good Fit

Get ready with a cloth, a bowl, or some kitchen paper towels and get into position to undo the screw anti-clockwise.

Place key Onto Radiator Bleed Screw And Use Something Absorbent Ready to Catch any Water Coming Out

Firmly undo the radiator bleed screw anti-clockwise until water is seen, or air/gas is heard hissing out of the radiator. If it is water catch the drips, if it is air, purge this out, and wait for the water to follow it. Catch the water drips and possibly put a bowl under the radiator where water may drip down it.

Undo Radiator Bleed Screw Anti-Clockwise, And Get Ready To Catch The Drips. Air Will Come Out First With A Hissing Noise, And Then Water Drips Out When Radiator Is Full

If very dirty water comes out, let it run for a while to clear, but use a bowl to catch the drips. If water squirts out at an angle, cover with a cloth to protect walls and furniture etc. and let this run down into the bowl. You can remove the screw if you are brave; but don’t let it shoot out and lose it!

Also be ready to catch the water right into a bowl, as it will squirt and spray out, possibly dirty if there has been no inhibitor installed into the system; tut tut!

Recheck the pressure…

Recheck The Water Pressure When Finished Bleeding The Radiators

In the case of open header tank, ball valve systems, check that the tank is hissing, and this will indicate that it is filling up because the ball valve is heard letting water into the system. (in the loft or airing cupboard, the small black tank like a toilet tank, not the cold tank of copper cylinder for the hot water if fitted)

In the case of a combi-boiler (combination boiler) locate the filling loop usually underneath the boiler…

Underneath The Average Combi Boiler; The Silver Braided Flexible Pipe Is The Filling Loop

Locate the tap and fill it until the gauge is correct again, and rebleed more radiators as above if required, and then repeat for each one, checking the pressure is correct. Do not overfill the system!