Can't bleed my system

[MikeM]

I have a Glow Worm 65-80 boiler system, pumped rads and thermo-syphon hot water. I drained system to move and replace the bathroom rad. I refilled the system and bled all rads. Now only downstairs rads work. When I bleed upstairs rads I sometimes get a little air out but the hot water is not reaching these rads. Also the syphon hot water system is not heating the water in the cylinder. I obviously have air trapped somewhere, I'd guess it may be in or above the boiler. As I have tried bleeding everything I can, where should I look next please?

I can't find any way to bleed the boiler itself.

 

[MANDATE]

Have you tried bleeding the pump?

 

[MikeM]

It's a Commodore 130 pump. There is a small screw either side of the main body casting, are these the bleed screws, or can I just slacken off the flow connection? Thanks!

 

[breezer]

is there not a big brass screw like the one in this picture?

to the right of the picture brass thing in the middle of black circle

 

[MANDATE]

I'm not familiar with your pump type, but I wouldn't think the two small screws are for bleeding. and I don't think slackening the flow or output connection would ensure the air is removed. I think it would depend on whether the pump is mounted horizontal or vertical.
On a horizontal mounted pump with the motor at the top you can understand a small air pocket gathering. On a vertical mounted pump I don't see how you have a air pocket. Unless of course your pipe work forms an inverted 'U' and on re filling water has entered from both sides and creating a large air pocket and the pump is revolving in air, but then downstairs rads would not work either.
To get rid of a large air lock using only the bleed valves would be difficult and time consuming because there is too much resistance. It is better to remove the radiator after closing the valves each side and run off a couple of bucket full of water from each side using a hose, this way there is no resistance to flow and the air is pushed along easily without the use of the pump.
Of course you will still have to bleed the rads again because some air will go in them.
Hope this helps

 

[MANDATE]

As an alternative to the above you could remove the plug from the top of the radiator opposite side to bleed off valve, screw in an adaptor ending with 15mm pipe and some clear plastic tubing and allow air and water to escape to bucket or bath. ( I've not tried this method, but it should work )