I'm having difficulting getting the radiators on the 2nd floor of our
house to heat up. My efforts have so far involved closing down the
LSVs almost completely on the hottest rads (kitchen area and ground
floor), leaving the LSVs wide open on the 2nd floor, and somewhere in
between on the 1st floor.

On balancing radiators, the FAQ says...

"The important thing is that the return water coming out of each
radiator is good and hot. If it's only warm you need to open its Lock
Shield Valve (LSV) some more, or if it's already wide open you have to
close the LSVs on the hottest radiators instead."

The problem is that the 2nd floor rads are still not hot (just warm),
and the ground and 1st floor rads now have cool return pipes. If I
open up the LSVs so get hot return pipes on the ground floor, then the
2nd floor rads are even less hot.

Do you think I need a bigger boiler (it's already a pretty big one)?
Or would a faster pump help?

Thanks,

Simon.