I've made my heating system worse!

[Rob Foster]

Thanks to everybody who offered advice, it's all been very helpful.
I've got about as much heat back in the problem rads as there was before I started changing valves by using a combination of the suggested techniques.
I think the problem mainly lies with undersized pipework so will take a stab at replacing the 10mm with 15mm in the warmer months.
Does anybody see any benefit to using something bigger than 15mm when that's what I'm going to be connecting it to?

Good plan, when it warms up get some dosh ready come back on and we will be pleased to help you, thanks for getting back. Rob Foster aka centralheatking

 

[Ivan Android]

Update: In the Summer I swapped out the 10mm with 15mm.
I had to surface mount the new pipes to the wall as I didn't fancy attempting to squeeze long lengths of 15mm down between the wall and the plasterboard. I covered them up with Talon double pipe covers and as the wall is white they look just fine.

It still took a few weeks for an airlock to work its way out of the system so I was a bit downhearted by the fact that the rads were not warming up much more than they had previously. Now though they are scorching, so much so that I think I'm going to need to reduce the flow a bit.

Thanks to all who got involved in this thread. The various comments and suggestions gave me the confidence that swapping out the 10mm pipe was the way to go.