Hi, xanderma,
You could certainly give the balancing method a try it may do the trick.
But i suspect that this may not be your problem. You see if a cleanser was not introduced to your system before it was drained down in the summer to enable your home improvements and a new dose of inhibitor put back in when it was refilled. Then i would guess that all the old sediment / sludge that has built up over the years has collected and lodged itself in bottom of your rads. ( If a cleanser had been used it would have stuck to the cleanser and simply flushed out ). And you now would not have a problem. So dont be suprised if the balancing trick does not work.
If balancing them fails, and you need some advice as how to get rid of the sludge / sediment then post again.