Radiators won’t get hot

[NODDYNODSVILLE]

Evening all.
I have open vented C/H system with a heat only boiler and 10 rads over 3 floors.
I have just replaced a rad on the middle floor. Drained system down for new gateway valve for cold feed for header tank. Refilled system no leaks, 👍, but the top top 2 rads won’t get hot.
ALL rads contain water, I have bled all rads. No hot water getting to flow pipe of either rad on top floor.
All other rads are working.
When I bleed the top cold rads, all I get is cold water.
Any ideas or help in helping me would be much appreciated
Simon

 

[SimonG]

I've said it before and will say it again.
Turn both valves off to radiators not working. Tray under one side and let water flow out of valve and into tray, decent amount of water as well. Then repeat at opposite end. Same with other radiator.

Had it before on 8mm, 10mm and 15mm pipe.

You say builder fitted loft rads? Plastic pipe?

 

[John.g]

I have got rid of air in one instance by just removing the 1 ins vent blanking plug at one end of the (modern) rad and giving each end a good flush through into a bucket.

 

[SimonG]

I have got rid of air in one instance by just removing the 1 ins vent blanking plug at one end of the (modern) rad and giving each end a good flush through into a bucket.

Done the same with a towel rail.

 

[NODDYNODSVILLE]

I've said it before and will say it again.
Turn both valves off to radiators not working. Tray under one side and let water flow out of valve and into tray, decent amount of water as well. Then repeat at opposite end. Same with other radiator.

Had it before on 8mm, 10mm and 15mm pipe.

You say builder fitted loft rads? Plastic pipe?

All copper as far as I can see.
Will get my buckets and towels ready

 

[John.g]

If your rads are like this you may find it easier to remove the Vent Plug after shutting the valves and first checking that the valves are holding by cracking open the vent then flush through the blank plug end from both sides. But if you think there is some crap in the pipework then the other method my be better.