Hmm
Combi's are usually sealed c/h systems, but not always.
Check boiler water pressure? Have you made sure you have filled it up through the filling loop with the same amount of water you drained out the radiator and the cold boiler pressure is set right for the boiler?
Normally most combis have an internal automatic by-pass valve, although on some systems you get an occasional rad with a set of permanently open lock shields to give another by pass.
The idea of balancing rads, is really to ensure even heating. It can be as simple as feeling the legs of the supply pipe's to the rad's to ensure they feel somewhere around even temp, with the locksheild side slightly cooler than the other. That is of course if the thermo valves are all on the flow or hot pipe.
But you can make a science of it, if you want to, but you need pipe thermometers to check your flow and return temps on each rad and the boiler are within the specification for the boiler and system.
However its also partly a design thing as well. In other words the pipework and rads at the system design stage has got to give you the correct flow and return temps after system heat losses are taken into account.
I'll stop there, your probably thinking, is it important?
Well yes, it obviously helps the boiler perform to its design criteria. And to low a temp difference on a condensing combi means its not condensing but acting like a normal combi.
And the clincher is, getting it right can save a bomb on running costs.
Incidentally condensing combis have a bigger temp drop than conventional ones.
I am sorry, I don't mean to sound as though I am giving you a lecture, its just the way I think of things.
There is plenty of good stuff on the internet about balancing CH systems, try them for a fuller explanation.
Incidentally its usually something you can do yourself its not hard to do, just a bit long winded to do it properly.
In point you can design systems without the need to balance them. You might even have one of those.
