Upstairs rads not getting hot

[SimonCentral]

Hello DIYnot folks,

I have been looking around the web for a definitive solution to my problem but so far I have come up a bit short and was hoping that by directly asking and laying out the system and symptoms that I might find some help... I appologise for the long post but thought it best you knew everything I have done etc.

The system:
'Standard' central heating system - header tank, combi boiler downstairs (getting on a bit) brand new pump (fitted vertically next to said boiler) 3 rads downstairs (piping hot) 5 rads upstairs (cold) If you need more info of this let me know specifics.

Problem:
Initially non of the central heating worked. On investigation the pump had seized. I removed the pump (didnt know about the cap and the fact I could have got it going with a screwdriver) and in removing the pump had to drain the system due to the tap above thre pump not seeming to stop the flow of water, so I drained it so I didnt get soaked.
On refitting the pump and filling up the system non of the upstairs rads got hot (fully blead of course) I have drained the system before and never had this problem, refitting the pump spawned it...

Things I have tried:
Since the problem first arose I checked the pump and found it to be a bit weak (wouldnt turn when started on setting I) I have bought a new, slightly more powerful pump - no change.
Completely drained the system again (ensuring all the downstairs rads were empty too), refilled, blead all rads (starting upstairs) - no change.
I have turned off all the downstairs rads and left it running for a few hours, checking for air in rads - no change.
All rads are fully open, both ends.

I have had signs of hot water upstairs in that when i drained approx 6 pints of water via the blead valve on what I believe to be the first rad upstairs (with the outlet valve closed) I got hot water to the feed pipe. I tried this on the bathroom rad too and felt heat on right hand pipe on the landing rad (thought that would be the outlet?) bit strange but thats what happened.

The only other thing I can report is that of the 5 rads upstairs 3 seem to have a fairly high pressure in them (noticable by the rate of air when bleading) where as ther other 2 dont (still filled up from empty and blead successfully) But this is probably due to them be further away from the boiler/pump?

With hot water circulating downstairs fine and a new pump fitted I can only deduce there is a airlock somewhere that is causing the problem. What do you think? If it is an airlock how do I shift it? I read somewhere about turing off all the fine ones (downstairs) and one tap on the problem rad(s) drain, fill, blead and repeat the process on the other valve... There is also a drain point below the pump but due to the squar nut being seived I have been unable to drain from there. Could this be an avenue?

If you got this far through my post I thank you! Any help on this would be really appreciated. The cold weather is drawing nearer and my 8 month old baby will suffer if I dont get this sorted. Last resort wil be to call a plumber in but the expence would kill me at the moment

 

[Boilerman2]

It sounds like there may be some air vents fitted to a high point somewhere on the pipework, you will have to trace pipes around the house and see if any highpoints in the pipes have a vent fitted
Unfortunately if fitted, they could be anywhere, (last one of these i had dealing with, I found two manual air Vents under the floor in front of the airing cupboard)