CH system airlock

[ed1178]

Can anyone help me shift a stubbon airlock?!

My central heating was working fine until recently when I drained the system in order to remove a few radiators whilst decorating. However on refilling only the upstairs rads get hot.

I have a pressurised system. Each rad has been bled several times and is full of water. I have bled the boiler heat exchanger and it too is full. The system pressure is correct at about 1.5 bar. The pump is working and the upstairs rads get hot within a few minutes as they should.

Downstairs I have 3 radiators which refuse to heat and 2 which work fine. I think the cold ones are supplied by a separate feed from the landing above and air is trapped here?

I have tried closing all the valves on all the radiators except one of the cold ones in order to force water through and air out, but this does not work even though the pump is running. There is a drain valve on the bottom of the feed to the cold radiators, this is full of water. I have tried opening it at the same time as the filling loop in order to push and air out but again had no luck.

The system is relatively new and was flushed after installation and had inhibitor added. More was added during refilling. On emptying the water was almost clear so I do not suspect a blockage.

I am now stuck for ideas - any help would be appreciated!

 

[misterdubya]

Turn off all warm rads
Turn pump up (if poss)
Ensure no H/w demand.
Close system bypass if it has one.

Should clear eventually.

 

[ed1178]

Thanks Misterdubya.

However have tried all of your suggestion previously to no avail. With the pump running on max, no DHW demand and all but one rad turned right off there was still joy even after a couple of hours. I tried this with each cold rad in turn again no luck.

I am not sure if I have a system bypass valve or not. Where would this be likely to be located? I think my boiler is a system type as it contains the pump, expansion vessel etc - would it be in here? It's a vokera unica HE. I am reluctant to lift floorbaords unless essential.

I read on another forum than one can try cooecting a hose to the system drain valve and forcing water through "backwards" - is this likely to help?