The automatic air valve is what it says " automatic " and has nothing to do with you re-pressurizing the system.
Assuming the radiator has been fitted back onto its pipework and the radiator bleed valve is closed. Open the two valves either end of the radiator. Open the filling loop taps and when the pressure gauge reaches 1 1/2 bar on the gauge close the filling loop taps.
DO NOT START YOUR BOILER AND THE PUMP YET
Next start bleeding your radiators starting with the ones downstairs. As you bleed air from a radiator tighten the bleed screw every now and then and check the pressure gauge ( NEVER LET IT REACH 0 ) if it has fallen slightly open the supply loop taps until the pressure gauge reads 1 1/2 bar on the gauge. Continue bleeding air from all the radiators ending with those upstairs ( air rises to the highest point in the system ).
When you have bled all the air out of your radiators open the bleed screw on the radiator nearest the boiler and allow water out of this bleed screw until the pressure gauge on the boiler reads 1 bar ( this is a standard pressure fore most combi boilers ).
You can now switch on the boiler and the water should circulate around the system ( because some air could have been trapped by bends in the pipework etc you may find it necessary to re-bleed the system in a few days ) , you will notice the pressure gauge reading will drop if this needs to be done.
The point of having an automatic air vent is to provide a means of ridding the sealed pipe system of any dissolved air within the water. ( If you boil an egg in a pan you will see air bubbles liberated from the water, when it is heated . The same happens in the sealed pipework of the CH system, the automatic air vent gets rid of this however the pressure within the system will then fall and you will need to open up the filling loop and pressurize the system to 1 bar again.
Every week check you boiler pressure and re-pressurize as required
If the tops of your radiators are cold whilst the bottoms are hot then you have air in the top half of your radiators and they need bleeding.
If the tops of your radiators are hot but the bottoms are cold, you have a build-up of sludge or rust in the radiators. The radiators can be removed and should either be flushed clear or replaced.
If either of these situations arises the system will again need re-pressurizing to 1 bar.
John ( Wirral ), August 2008
