how can I fix my oil fired boiler - valliant f75-4?

I just recently had anti freeze put into the boiler, there are two zones. One regulator is hot, the other is luke warm producing no heat in the base board rads. the other is producing heat but rads in that zone are not as hot should be. Example- when touching the pipes in the basement they are hot to touch but not producing much heat when touched up stairs at the rads.