If I want to force pump to direct all its attention to radiator in loft to see if I can get them hot. Will simply turning down the thermostatic valves for all the other radiators have that affect or do I also need to close the lockshield valves as well
Edit, update explanation of my system
I am based in Uk with three storey house. I have a 2 year old Worcester Bosch 24R Boiler, There is a 22mm supply and 22m return copper pipe round along the first floor floor joists from left to right through the house, with a pump on the supply pipe near the boiler. The supply pipe serves both the Central Heating and Heating a regular Hot Water Cylinder, I can control whether to use CH, Hot Water or both, there is a T-valve near the the hot water cylinder that controls this.
On the first floor there are 15mm copper pipes that come off the 22m supply and back onto the return, the same downstairs. Evey radiator has its own loop.
The only slight problem with this arrangement is that the T-Valve is positioned after two downstairs radiators have been supplied, so unless I turn them off they are always heated even if only specify Hot water.
In contrast there are two radiators on the 3rd floor (but still top of radiator is 1.5m below feed/expansion tank in loft) supplied by plastic pipe, although it doe seem to also be 15mm. What I can see is there is one set of pipes shared between the two radiators so I guess this halves the flow immediately ?
What I cannot readily see because I would have to remove bathroom laminate flooring is where they join the 22mm pipe, there is a possibility that they are sharing a loop with bathroom radiator.
The radiator that I described as further away, and you say nearer is physically quite far from the boiler (i.e start of 22mm supply pipe), but is probably nearest to somewhere along the 22mm supply pipe. So what is (most)important , distance to start of supply pipe or distance to supply pipe ?
I did consider whether to replace the plastic pipes with two set of pipes and that would be quite easy, however there would still be a short run under the bathroom floor of one 15mm pipe to the 22mm pipe, so if any of the pipe run is shared would that mean having two sets of pipes further up would have no effect.
All of the radiators and valves have recently been replaced ( 2 weeks ago) so there is no issue with sludge in bottom of radiator and unlikely to be problem with valves. Actually last night one of the radiators did get warm (but no hot) throughout, but the other failed for warm at all. I bled them again and there was no air, there was water.