Try this... get the instruction manual for your boiler and find out how to get in to the D codes, when you have go to D0 and reduce the output to 24 and see if your rads heat any better, chances are that you will have to upgrade the pump regardless.
Hi I tried this and it made little or no change.
as I said earlier close coupled tees or a low loss header,
Where would I install the low loss header? The cyclinder is approximately 100 sq ft away from the boiler.
The UFH install sounds like a massive lashup as well- take it there's a single loop, no manifold, no bypass?
Where would I install the manifold and thermostat to this now? Next to the boiler or in the UFH room?